Carbene-functionalized composite materials

ABSTRACT

The present application provides stable, carbene-functionalized composite materials, and methods and uses thereof. These carbene-functionalized composite materials comprise a material having a metal surface, and a carbene monolayer that is uniform, contaminant-free (metal oxide, etc), and more stable than thiol-functionalized monolayers. Uses of such carbene-functionalized composite materials include semi-conducting materials, microelectronic devices, drug delivery or sensing applications.

RELATED APPLICATIONS

This application claims the benefit of the filing dates of U.S.Provisional Patent Application No. 61/867,466, filed on Aug. 19, 2013,and U.S. Provisional Patent Application No. 62/018,782, filed on Jun.30, 2014, the contents of which are incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The present application pertains to the field of materials science. Moreparticularly, the present application relates to carbene-functionalizedcomposite materials.

BACKGROUND

Self-assembled monolayers (SAMs) on metals such as gold have potentialapplication in sensing, electrochemistry, drug delivery, surfaceprotection, microelectronics and microelectromechanical systems, amongothers [R. G. Nuzzo, et al. J. Am. Chem. Soc. 105, 4481 (1983); B. D.Gates, et al. Chem. Rev. 105, 1171 (2005); J. C. Love, et al. Chem. Rev.105, 1103 (2005); U. Drechsler, et al. Chem.—Eur. J. 10, 5570 (2004)].Since a discovery of sulfur-based SAMs on gold [C. D. Bain et al. J. Am.Chem. Soc. 111, 321 (1989)], suitable alternatives for these ligandshave not been found, despite the thiol-based SAMs' oxidative and thermalinstability on gold being a significant impediment to their widespreaduse [C. Vericat, et al. Chem. Soc. Rev. 39, 1805 (2010)]. Thiol-basedSAMs are stable when stored in ultra high vacuum in an absence of light[J. Noh, et al. J. Phys. Chem. B 110, 2793 (2006)], however degradationhas been observed after as little as one to two weeks at roomtemperature in air [C. Vericat, et al. J. Phys. Condens. Matter 20,184004 (2008); Y. Li, et al. J. Am. Chem. Soc. 114, 2428 (1992); M. H.Schoenfisch, et al. J. Am. Chem. Soc. 120, 4501 (1998); J. B. Schlenoff,et al. J. Am. Chem. Soc. 117, 12528 (1995)]. Improvements in stabilitycan be accomplished by changing the gold surface's nature [C. Vericat,et al. J. Phys. Condens. Matter 20, 184004 (2008)], by addition ofadditives [G. Yang, et al. Langmuir 20, 3995 (2004)], or through use ofmulti-dentate thio-adsorbates [P. Chinwangso, A. C. Jamison, T. R. Lee,Accounts of Chemical Research, 44, 511 (2011)]. Phosphine-based ligandshave also been examined, but offer weaker bonds to a surface [A. D.Jewell, et al. Phys. Rev. B 82, 205401 (2010)].

Carbon-based ligands known as N-heterocyclic carbenes (NHCs) have playeda role in the field of transition metal complexes [W. A. Herrmann,Angew. Chem. Int. Ed. 41, 1290 (2002); E. Peris, et al. Coord. Chem.Rev. 248, 2239 (2004)]. These ligands are part of catalysts such as theGrubbs second generation metathesis catalyst [R. M. Thomas, et al.Organometallics 30, 6713 (2011)], and NHC-based cross-coupling catalysts[E. A. B Kantchev, et al. Angew. Chem. Int. Ed. 46, 2768 (2007)]. Unlikemost carbenes, which are reactive with limited stability, NHCs typicallyhave one or two heteroatoms adjacent to a carbene carbon [A. Igau, etal. J. Am. Chem. Soc. 110, 6463 (1988); A. J. Arduengo, et al. J. Am.Chem. Soc. 113, 361 (1991)]. These heteroatoms increase NHCs' stabilitysuch that they can usually be prepared on a gram scale [M. Niehues, etal. Organometallics 21, 2905 (2002)], crystallized [A. J. Arduengo, R.L. Harlow, M. Kline, J. Am. Chem. Soc. 113, 361 (1991)], distilled [M.Niehues, et al. Organometallics 21, 2905 (2002)], and stored for longerperiods of time [4 years, when stored under N₂ in a freezer]. An Au-NHCbond is estimated to be on an order of 90 kJ/mol stronger than acorresponding Au-phosphine bond, and twice as strong as metal sulfidebonds in molecular complexes [P. Pyykkö, et al. Chem. Asian J. 1, 623(2006)]. As such, NHCs have potential to be valuable ligands forprotecting and functionalizing gold and other metal surfaces.Application of these carbenes in materials science, and other fieldsoutside of homogeneous catalysis, has been limited [L. Mercs, et al.Chem. Soc. Rev. 39, 1903 (2010)].

The above information is provided for the purpose of making knowninformation believed by the applicant to be of possible relevance to thepresent invention. No admission is necessarily intended, nor should beconstrued, that any of the preceding information constitutes prior artagainst the present invention.

SUMMARY OF THE INVENTION

An aspect of the application is to provide carbene-functionalizedcomposite materials and methods of manufacture thereof. In accordancewith one aspect, there is provided a carbene-functionalized compositematerial, comprising a carbene monolayer, and a material having at leasta metal surface, wherein the carbene monolayer interacts with the metalsurface and is stable, uniform, and/or substantially free ofcontamination. In one embodiment, the carbene monolayer comprises ≤5%,or ≤2% contamination.

In accordance with another embodiment, the carbene monolayer comprisesone or more carbenes of formula I

wherein:

-   -   n is an integer from 1 to 8, or from 1 to 4;    -   m is an integer from 0 to 4;    -   A is absent, an aliphatic cycle, a heterocycle, an aromatic        ring, a fused aromatic ring system, a heteroaromatic ring,        and/or a fused heteroaromatic ring system, each of which is        optionally substituted;    -   X-L-Z is absent, or    -   X is C or a heteroatom,    -   L is a divalent moiety, such as C₁-C₁₀ alkylene, C₁₀-C₂₀        alkylene, C₁-C₁₀ alkenylene, C₁₀-C₂₀ alkenylene, C₁-C₁₀        alkynylene, C₁₀-C₂₀ alkynylene, or dextran, a simple sugar,        complex sugar, carbohydrate, ether, thioether, amine, polyamine,        polyether, and/or polythioether, each of which is optionally        substituted;    -   Z is H, an aliphatic cycle, a heterocycle, an aromatic ring, a        fused aromatic ring system, a heteroaromatic ring, a fused        heteroaromatic ring system, an organometallic complex, a        transition-metal catalyst, a metal-oxide catalyst, a simple        sugar, a complex sugar, a carbohydrate, or a chemically        derivatizable group, such as —OH, azide, carboxylic acid,        carbonyl chloride, anhydride, ester, aldehyde, alcohol, amine,        halogen, epoxide, thiirane, aziridine, amino acid, nucleic acid,        alkene, alkyne, conjugated diene, thiol, or thioester, each of        which is optionally substituted;    -   each Y or Y′ is independently C or a heteroatom;    -   each R^(∘) is independently H, halogen, the substituent X-L-Z as        defined above, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, or C₁₀-C₂₀ alkynyl, C₁-C₁₀        alkoxyl, C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic moiety, aryl,        heteroaryl, ether, thioether, amine, polyamine, polyether, or        polythioether, each of which is optionally substituted; or, two        of R^(∘), together with the atoms to which they are attached,        are connected to form a cycle, or heterocycle, each of which is        optionally substituted; and    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkylC₁-C₁₀ alkenyl, C₁₀-C₂₀        alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₃-C₂₀ cyclic        aliphatic moiety, aryl, heteroaryl, ether, thiol, thioether,        amine, polyamine, polyether, polythioether, or polythiol, each        of which is optionally substituted; or, one of R¹ or R², with        one of R^(∘), together with the atoms to which they are        attached, are connected to form a cycle, or heterocycle, each of        which is optionally substituted;    -   wherein, when A is absent or non-aromatic, the dashed line        represents an optional double bond; and/or    -   when A is absent, each Y′ is independently bonded to R^(∘) or        X-L-Z, as defined above.

In accordance with another embodiment, the carbene monolayer comprisesone or more carbenes of formula Ia

wherein:

-   -   m is an integer from 0 to 4;    -   each Y is independently C or a heteroatom;    -   Y² and Y³ are independently C or a heteroatom, and the dashed        line represents an optional double bond;    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₃-C₂₀ cyclic        aliphatic moiety, aryl, heteroaryl, ether, thiol, thioether,        amine, polyamine, polyether, polythioether, or polythiol, each        of which may be optionally substituted;    -   R³ and R⁴ are independently H, halogen, the substituent X-L-Z as        defined for Formula I, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀        alkenyl, C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl,        C₃-C₂₀ cyclic aliphatic moiety, C₁-C₁₀ alkoxyl, C₁₀-C₂₀ alkoxyl,        C₃-C₂₀ cyclic aliphatic moiety, aryl, heteroaryl, ether,        thioether, amine, polyamine, polyether, or polythioether, each        of which is optionally substituted; or, any one of R³ or R⁴,        with any one of R¹ or R², together with the atoms to which they        are attached, are connected to form a cycle, or heterocycle,        each of which is optionally substituted.

In accordance with another aspect, there is provided a method forforming a composite material comprising a carbene monolayer and amaterial having at least a metal surface, wherein the carbene monolayerinteracts with the metal surface and is stable, uniform, and/orsubstantially free of contamination, said method comprising contacting ametal surface with at least one carbene or carbene precursor.

In accordance with one embodiment, contacting a metal surface with atleast one carbene or carbene precursor comprises immersing said surfacein carbenes or carbene precursors; or, thermally decomposing carbeneprecursors in the presence of said surface.

In accordance with one embodiment of this method, the carbenes are offormula I or formula Ia. In accordance with another embodiment, one ofthe carbene precursors is of formula II

wherein:

-   -   n is an integer from 1 to 8, or from 1 to 4;    -   m is an integer from 0 to 4;    -   B is a counter ion that optionally acts as a base;    -   A is absent, an aliphatic cycle, a heterocycle, an aromatic        ring, a fused aromatic ring system, a heteroaromatic ring,        and/or a fused heteroaromatic ring system, each of which is        optionally substituted;    -   X-L-Z is absent, or    -   X is C or a heteroatom,    -   L is a divalent moiety, such as C₁-C₁₀ alkylene, C₁₀-C₂₀        alkylene, C₁-C₁₀ alkenylene, C₁₀-C₂₀ alkenylene, C₁-C₁₀        alkynylene, C₁₀-C₂₀ alkynylene, or dextran, a simple sugar,        complex sugar, carbohydrate, ether, thioether, amine, polyamine,        polyether, and/or polythioether, each of which is optionally        substituted;    -   Z is H, an aliphatic cycle, a heterocycle, an aromatic ring, a        fused aromatic ring system, a heteroaromatic ring, a fused        heteroaromatic ring system, an organometallic complex, a        transition-metal catalyst, a metal-oxide catalyst, a simple        sugar, a complex sugar, a carbohydrate, or a chemically        derivatizable group, such as —OH, azide, carboxylic acid,        carbonyl chloride, anhydride, ester, aldehyde, alcohol, amine,        halogen, epoxide, thiirane, aziridine, amino acid, nucleic acid,        alkene, alkyne, conjugated diene, thiol, or thioester, each of        which is optionally substituted;    -   each Y or Y′ is independently C or a heteroatom;    -   each R^(∘) is independently H, halogen, the substituent X-L-Z as        defined above, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₁-C₁₀ alkoxyl,        C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic moiety, aryl,        heteroaryl, ether, thioether, amine, polyamine, polyether, or        polythioether, each of which is optionally substituted; or, two        of R^(∘), together with the atoms to which they are attached,        are connected to form a cycle, or heterocycle, each of which is        optionally substituted; and    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₃-C₂₀ cyclic        aliphatic moiety, aryl, heteroaryl, ether, thiol, thioether,        amine, polyamine, polyether, polythioether, or polythiol, each        of which is optionally substituted; or, one of R¹ or R², with        one of R^(∘), together with the atoms to which they are        attached, are connected to form a cycle, or heterocycle, each of        which is optionally substituted;    -   wherein, when A is absent or non-aromatic, the dashed line        represents an optional double bond; and/or    -   when A is absent, each Y′ is independently bonded to R^(∘) or        X-L-Z, as defined above.

In accordance with an another embodiment of this method, the carbeneprecursor is of formula IIa

wherein:

-   -   m is an integer from 0 to 4;    -   B is a counter ion that optionally acts as a base;    -   each Y is independently C or a heteroatom;    -   Y² and Y³ are independently C or a heteroatom, and the dashed        line is an optional double bond;    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl), cycloalkyl,        aryl, heteroaryl, ether, thiol, thioether, amine, polyamine,        polyether, polythioether, or polythiol, each of which is        optionally substituted;    -   R³ and R⁴ are independently H, halogen, the substituent X-L-Z as        defined for Formula II, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀        alkenyl, C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl,        C₁-C₁₀ alkoxyl, C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic, aryl,        heteroaryl, ether, thioether, amine, polyamine, polyether, or        polythioether, each of which is optionally substituted; or, any        one of R³ or R⁴, with any one of R¹ or R², together with the        atoms to which they are attached, are connected to form a cycle,        or heterocycle, each of which is optionally substituted.

In accordance with an alternative embodiment of this method, the carbeneprecursor is of formula III

wherein:

-   -   n is an integer from 1 to 4, or alternatively 1 to 8;    -   m is an integer from 0 to 4;    -   G is a perhalogenated alkyl, perhalogenated alkenyl,        perhalogenated alkynyl, a perhalogenated aryl, or OR′, wherein        R′ is an aliphatic group, for example, an alkyl group.    -   A is absent, an aliphatic cycle, a heterocycle, an aromatic        ring, a fused aromatic ring system, a heteroaromatic ring,        and/or a fused heteroaromatic ring system, each of which is        optionally substituted;    -   X-L-Z is absent, or    -   X is C or a heteroatom,    -   L is a divalent moiety, such as C₁-C₁₀ alkylene, C₁₀-C₂₀        alkylene, C₁-C₁₀ alkenylene, C₁₀-C₂₀ alkenylene, C₁-C₁₀        alkynylene, C₁₀-C₂₀ alkynylene, or dextran, a simple sugar,        complex sugar, carbohydrate, ether, thioether, amine, polyamine,        polyether, and/or polythioether, each of which is optionally        substituted;    -   Z is H, an aliphatic cycle, a heterocycle, an aromatic ring, a        fused aromatic ring system, a heteroaromatic ring, a fused        heteroaromatic ring system, an organometallic complex, a        transition-metal catalyst, a metal-oxide catalyst, a simple        sugar, a complex sugar, a carbohydrate, or a chemically        derivatizable group, such as —OH, azide, carboxylic acid,        carbonyl chloride, anhydride, ester, aldehyde, alcohol, amine,        halogen, epoxide, thiirane, aziridine, amino acid, nucleic acid,        alkene, alkyne, conjugated diene, thiol, alkyl thiol, or        thioester, each of which is optionally substituted;    -   each Y or Y′ is independently C or a heteroatom;    -   each R^(∘) is independently H, halogen, the substituent X-L-Z as        defined above, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, or C₁₀-C₂₀ alkynyl, C₁-C₁₀        alkoxyl, C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic moiety, aryl,        heteroaryl, ether, thioether, amine, polyamine, polyether, or        polythioether, each of which is optionally substituted; or, two        of R^(∘), together with the atoms to which they are attached,        are connected to form a cycle, or heterocycle, each of which is        optionally substituted; and    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, branched C₁-C₁₀        alkyl, C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, or C₁₀-C₂₀ alkynyl),        C₃-C₂₀ cyclic aliphatic moiety, aryl, heteroaryl, ether, thiol,        thioether, amine, polyamine, polyether, polythioether, or        polythiol, each of which is optionally substituted; or, one of        R¹ or R², with one of R^(∘), together with the atoms to which        they are attached, are connected to form a cycle, or        heterocycle, each of which is optionally substituted;    -   wherein, when A is absent or non-aromatic, the dashed line        represents an optional double bond; and/or    -   when A is absent, each Y′ is independently bonded to R^(∘) or        X-L-Z, as defined above.

In accordance with an another embodiment of this method, the carbeneprecursor is of formula IIIa

wherein:

-   -   m is an integer from 0 to 4;    -   G is a perhalogenated alkyl, perhalogenated alkenyl,        perhalogenated alkynyl, a perhalogenated aryl, or OR′, wherein        R′ is an aliphatic group, for example, an alkyl group.    -   each Y or Y′ is independently C or a heteroatom;    -   Y² and Y³ are independently C or a heteroatom, and the dashed        line represents an optional double bond;    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, cycloalkyl,        aryl, heteroaryl, ether, thiol, thioether, amine, polyamine,        polyether, polythioether, or polythiol, each of which may be        optionally substituted;    -   R³ and R⁴ are independently H, halogen, the substituent X-L-Z as        defined for Formula III, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, branched        C₁-C₁₀ alkyl, branched C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl, C₁₀-C₂₀        alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₁-C₁₀ alkoxyl,        C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic, aryl, heteroaryl,        ether, thioether, amine, polyamine, polyether, or polythioether,        each of which is optionally substituted; or, any one of R³ or        R⁴, with any one of R¹ or R², together with the atoms to which        they are attached, are connected to form a cycle, or        heterocycle, each of which is optionally substituted.

In accordance with another aspect, there is provided a method forforming a composite material comprising a carbene monolayer and amaterial having at least a metal surface, wherein the carbene monolayerinteracts with the metal surface and is stable, uniform, and/orsubstantially free of contamination, said method comprising vapourdepositing a carbene or carbene precursor on a metal surface.

In accordance with another aspect, there is provided a method forremoving a carbene-monolayer from a composite material, wherein saidcomposite material comprises said carbene monolayer and a materialhaving at least a metal surface, wherein the carbene monolayer interactswith the metal surface and is stable, uniform, and/or substantially freeof contamination, said method comprising exposing the composite materialto a >1% H₂O₂ solution for at least 24 h; or exposing the compositematerial to temperatures≥190° C. in a suitable solvent. In oneembodiment, the suitable solvent is decalin.

In accordance with another aspect of the application, there is provideda use of the herein described carbene-functionalized composite materialsfor modifying a metal surface.

In accordance with another aspect, there is provided acarbene-functionalized composite material comprising, a lipid layer, ahydrophobic carbene monolayer that is uniform, stable, and/orsubstantially free of contamination; and a material having at least onemetal surface, wherein said hydrophobic carbene monolayer interacts withthe metal surface, and said hydrophobic carbene monolayer is between thelipid layer and the metal surface. In accordance with one embodiment,the material is a metal chip and the composite material forms at leastpart of an analytical instrument. In another embodiment, the metal chipcomprises a metal film and all connections necessary for incorporationinto an analytical instrument as a detector.

In accordance with another embodiment, the carbene monolayer comprisesone or more carbenes of formula IV

wherein:

-   -   n is an integer from 1 to 8, or from 1 to 4;    -   m is an integer from 0 to 4;    -   A is absent, an aliphatic cycle, a heterocycle, an aromatic        ring, a fused aromatic ring system, a heteroaromatic ring,        and/or a fused heteroaromatic ring system, each of which is        optionally substituted;    -   X-L-Z is absent, or    -   X is C or a heteroatom,    -   L is a divalent moiety, such as C₁₀-C₂₀ alkylene, C₁₀-C₂₀        alkenylene, C₁₀-C₂₀ alkynylene, dextran, a simple sugar, complex        sugar, carbohydrate, ether, thioether, polyether, and/or        polythioether, each of which is optionally substituted;    -   Z is H or L, as defined above;    -   each Y or Y′ is independently C or a heteroatom;    -   each R^(∘) is independently H, halogen, the substituent X-L-Z as        defined above, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₁₀-C₂₀ alkoxyl, C₆-C₂₀ cyclic aliphatic moiety, aryl, ether,        thioether, polyether, or polythioether, each of which is        optionally substituted; or, two of R^(∘), together with the        atoms to which they are attached, are connected to form a cycle,        which is optionally substituted; and    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₆-C₂₀ cyclic aliphatic moiety, aryl, ether, thiol, thioether,        polyether, polythioether, or polythiol, each of which is        optionally substituted; or, one of R¹ or R², with one of R^(∘),        together with the atoms to which they are attached, are        connected to form a cycle, which is optionally substituted;    -   wherein, when A is absent or non-aromatic, the dashed line        represents an optional double bond; and/or    -   when A is absent, each Y′ is independently bonded to R^(∘) or        X-L-Z, as defined above.

In accordance with another embodiment, the carbene monolayer comprisesone or more carbenes of formula IVa

wherein:

-   -   m is an integer from 0 to 4;    -   each Y is independently C or a heteroatom;    -   Y² and Y³ are independently C or a heteroatom, and the dashed        line represents an optional double bond;    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₆-C₂₀ cyclic aliphatic moiety, aryl, ether, thiol, thioether,        polyether, polythioether, or polythiol, each of which may be        optionally substituted;    -   R³ and R⁴ are independently H, the substituent X-L-Z as defined        for Formula IV, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₆-C₂₀ cyclic aliphatic moiety, C₁₀-C₂₀ alkoxyl, aryl, ether,        thioether, polyether, or polythioether, each of which is        optionally substituted; or, any one of R³ or R⁴, with any one of        R¹ or R², together with the atoms to which they are attached,        are connected to form a cycle, which is optionally substituted.

In accordance with another aspect, there is provided a method forforming a carbene-functionalized composite material comprising, a lipidlayer, a hydrophobic carbene monolayer that is uniform, stable, and/orsubstantially free of contamination; and a material having at least onemetal surface, wherein said hydrophobic carbene monolayer interacts withthe metal surface, and said hydrophobic carbene monolayer is between thelipid layer and the metal surface, said method comprising contacting thematerial with a carbene or carbene precursor; and exposing thecarbene-coated material to lipid vesicles.

In one embodiment on this method, the carbene is of formula IV and IVa.In another embodiment of this method, the carbene precursor is offormula V

wherein:

-   -   n is an integer from 1 to 8, or from 1 to 4;    -   m is an integer from 0 to 4;    -   B is a counter ion that optionally acts as a base;    -   A is absent, an aliphatic cycle, a heterocycle, an aromatic        ring, a fused aromatic ring system, a heteroaromatic ring,        and/or a fused heteroaromatic ring system, each of which is        optionally substituted;    -   X-L-Z is absent, or    -   X is C or a heteroatom,    -   L is a divalent moiety, such as C₁₀-C₂₀ alkylene, C₁₀-C₂₀        alkenylene, C₁₀-C₂₀ alkynylene, dextran, a simple sugar, complex        sugar, carbohydrate, ether, thioether, polyether, and/or        polythioether, each of which is optionally substituted;    -   Z is H or L, as defined above;    -   each Y or Y′ is independently C or a heteroatom;    -   each R^(∘) is independently H, halogen, the substituent X-L-Z as        defined above, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₁₀-C₂₀ alkoxyl, C₆-C₂₀ cyclic aliphatic moiety, aryl, ether,        thioether, polyether, or polythioether, each of which is        optionally substituted; or, two of R^(∘), together with the        atoms to which they are attached, are connected to form a cycle,        which is optionally substituted; and    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₆-C₂₀ cyclic aliphatic moiety, aryl, ether, thiol, thioether,        polyether, polythioether, or polythiol, each of which is        optionally substituted; or, one of R¹ or R², with one of R^(∘),        together with the atoms to which they are attached, are        connected to form a cycle, which is optionally substituted;    -   wherein, when A is absent or non-aromatic, the dashed line        represents an optional double bond; and/or    -   when A is absent, each Y′ is independently bonded to R^(∘) or        X-L-Z, as defined above.

In accordance with another embodiment, the carbene precursor is offormula Va

wherein:

-   -   m is an integer from 0 to 4;    -   B is a counter ion that optionally acts as a base;    -   each Y is independently C or a heteroatom;    -   Y² and Y³ are independently C or a heteroatom, and the dashed        line is an optional double bond;    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₆-C₂₀ cyclic aliphatic moiety, aryl, ether, thiol, thioether,        polyether, polythioether, or polythiol, each of which may be        optionally substituted;    -   R³ and R⁴ are independently H, the substituent X-L-Z as defined        for Formula V, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₆-C₂₀ cyclic aliphatic moiety, C₁₀-C₂₀ alkoxyl, aryl, ether,        thioether, polyether, or polythioether, each of which is        optionally substituted; or, any one of R³ or R⁴, with any one of        R¹ or R², together with the atoms to which they are attached,        are connected to form a cycle, which is optionally substituted.

In accordance with an alternative embodiment of this method, the carbeneprecursor is of formula VI

wherein:

-   -   n is an integer from 1 to 4, or alternatively 1 to 8;    -   m is an integer from 0 to 4;    -   G is a perhalogenated alkyl, perhalogenated alkenyl,        perhalogenated alkynyl, a perhalogenated aryl, or OR′, wherein        R′ is an aliphatic group, for example, an alkyl group.    -   A is absent, an aliphatic cycle, a heterocycle, an aromatic        ring, a fused aromatic ring system, a heteroaromatic ring,        and/or a fused heteroaromatic ring system, each of which is        optionally substituted;    -   X-L-Z is absent, or    -   X is C or a heteroatom,    -   L is a divalent moiety, such as C₁₀-C₂₀ alkylene, C₁₀-C₂₀        alkenylene, C₁₀-C₂₀ alkynylene, dextran, a simple sugar, complex        sugar, carbohydrate, ether, thioether, polyether, and/or        polythioether, each of which is optionally substituted;    -   Z is H or L, as defined above;    -   each Y or Y′ is independently C or a heteroatom;    -   each R^(∘) is independently H, halogen, the substituent X-L-Z as        defined above, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₁₀-C₂₀ alkoxyl, C₆-C₂₀ cyclic aliphatic moiety, aryl, ether,        thioether, polyether, or polythioether, each of which is        optionally substituted; or, two of R^(∘), together with the        atoms to which they are attached, are connected to form a cycle,        which is optionally substituted; and    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₆-C₂₀ cyclic aliphatic moiety, aryl, ether, thiol, thioether,        polyether, polythioether, or polythiol, each of which is        optionally substituted; or, one of R¹ or R², with one of R^(∘),        together with the atoms to which they are attached, are        connected to form a cycle, which is optionally substituted;    -   wherein, when A is absent or non-aromatic, the dashed line        represents an optional double bond; and/or    -   when A is absent, each Y′ is independently bonded to R^(∘) or        X-L-Z, as defined above.

In accordance with another alternative embodiment, the carbene precursoris of formula VIa

wherein:

-   -   m is an integer from 0 to 4;    -   G is a perhalogenated alkyl, perhalogenated alkenyl,        perhalogenated alkynyl, a perhalogenated aryl, or OR′, wherein        R′ is an aliphatic group, for example, an alkyl group.    -   each Y or Y′ is independently C or a heteroatom;    -   Y² and Y³ are independently C or a heteroatom, and the dashed        line represents an optional double bond;    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀ alkynyl,        C₆-C₂₀ cyclic aliphatic moiety, aryl, ether, thiol, thioether,        polyether, polythioether, or polythiol, each of which may be        optionally substituted;    -   R³ and R⁴ are independently H, the substituent X-L-Z as defined        for Formula VIa, C₁₀-C₂₀ alkyl, C₁₀-C₂₀ alkenyl, C₁₀-C₂₀        alkynyl, C₆-C₂₀ cyclic aliphatic moiety, C₁₀-C₂₀ alkoxyl, aryl,        ether, thioether, polyether, or polythioether, each of which is        optionally substituted; or, any one of R³ or R⁴, with any one of        R¹ or R², together with the atoms to which they are attached,        are connected to form a cycle, which is optionally substituted.

In accordance with another aspect, there is provided a use of the hereindescribed carbene-functionalized composite materials in detecting andsensing applications. In one embodiment, the applications comprisedetecting biomolecules.

BRIEF DESCRIPTION OF TABLES and FIGURES

For a better understanding of the present invention, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingtables and drawings, where:

Table 1 presents structural information on the herein described NHCs onmetal;

Table 2A presents expected and found N:C ratios from C and N XPS spectrafor carbene terminated gold (Au(111) and Au(NP) where the carbenemonolayer is self-assembled from various NHCs. These data suggest aclean transfer of NHCs to surfaces was obtained for both Au(111) and Aunanoparticles;

Table 2B presents C and N XPS spectra for carbene terminated gold (Au(111)) where the carbene monolayer is self-assembled from carbonatesalts of various NHCs. These data suggest a clean transfer of NHCs tosurfaces;

Table 3 is shown in FIG. 23.

Table 4 presents characterization data of a representative NHC onPalladium (Pd) nanoparticles;

Table 5A presents a comparison loading of lecithin vesicles on acommercial HPA sensor chip and a representative NHC sensor chip. Thesedata suggest that the NHC sensor chip offers improved performance ascompared to the commercial sensor chip; and

Table 5B presents a comparison of stability between an HPA sensor chipand a representative NHC sensor chip. These data suggest that the NHCsensor chip is stable under conditions that could destroy or damage acommercial sensor chip.

FIG. 1A depicts reaction of free carbene NHC-1 (see Table 1) withdodecylsulfide-protected Au surfaces, which resulted in displacement ofsulfide. Once formed, NHC-protected surfaces did not show incorporationof sulfur upon treatment with dodecyl sulfide or dodecanethiol under theconditions specified as determined by XPS analysis;

FIG. 1B depicts N(1s), C(1s) and S(2p) XPS spectra of the product of theforward direction reaction shown in FIG. 1A (Au_(NP)(NHC-1)). Loss ofdodecylsulfide is demonstrated by a lack of S(2p) signal;

FIGS. 1C and 1D depict XPS spectra of the product of Au_(NP)(NHC-1)(FIG. 1C) and Au(111)(NHC-1) (FIG. 1D) exposed to S(C₁₂H₂₅)₂ as shown inthe reverse reaction in FIG. 1A. In both cases, lack of incorporation ofdodecylsulfide is demonstrated by the absence of S(2p) signal, whileretention of the NHC is demonstrated by the expected N(1s)/C(1s) arearatio;

FIG. 2A depicts an STM image of NHC-1 on Au(111) that showed orderedself-assembly where rows of 5-10 oval shaped features were observed,consistent with the presence of stacked units of benzimidazole NHCs onthe surface (dark regions represent one atom-deep erosion of the surfaceanalogous to those seen with thiol-based monolayers);

FIG. 2B depicts an STM image of the monolayer prepared from thecarbonate salt of NHC-1 on Au(111) demonstrating highly orderedself-assembly. A repeating lattice unit 2.65 times the length of theunderlying Au lattice was observed. In each repeat unit, bright regionscorresponded to the NHC molecule, while the dark regions represented theunderlying Au layer;

FIG. 2C depicts N(1s) and C(1s) XPS data that indicate chemicalstability of NHC-1 on Au(111) to treatment with boiling non-aqueous andaqueous solutions (left and centre), and only slight erosion of thesurface after treatment with 1% H₂O₂ for 24 h (right);

FIG. 2D depicts N(1s) and C(1s) XPS data that indicate completestability of NHC-3 on Au(111) films (see Table 1) in hot solvent (left),but decomposition of the film in boiling water (right), which isindicative of a lower stability of surfaces formed from NHC-3;

FIG. 2E depicts representative XPS data for the treatment ofNHC-1-terminated Au(111) surfaces with 1 mM solutions of dodecanethiolfor 24 h at room temperature; the XPS spectra showed no S(2p) signal,indicating no thiol incorporation, while the N(1s) and C(1s) spectrasuggest that the NHC-1 remained bound;

FIG. 3A depicts the reaction of azide-terminated NHC-6 with Au(111) (seeTable 1) and subsequent conversion into a triazole by a Cu-catalyzedclick reaction with propargyl alcohol;

FIG. 3B depicts XPS measurements on the azide-terminated NHC surfacethat showed a contact angle of 78±3°, and XPS analysis of the surfaceshowed three N signals as expected: one for the two virtually equivalentnitrogen atoms of the NHC portion, one for the central nitrogen of theazide (at approximately 406 eV) and one signal for the remaining two,highly similar nitrogen atoms of the azide;

FIG. 3C depicts XPS measurements of the same surface after reaction withpropargyl alcohol; the contact angle decreased to 45±3°, consistent withan alcohol-terminated surface and the XPS analysis of N(1s) changed,indicating triazole formation, such that only two types of N atoms wereobserved and the diagnostic, central N atom of the azide at 406 eV wasabsent;

FIG. 3D depicts representative XPS data for the treatment ofdodecanethiol-protected Au(111) surfaces with solutions of NHC-1 for 24h at room temperature; the XPS spectra showed that approximately 40% ofthe S(2p) signal remained (the asymmetric peak was due to the presenceof two electronic states, S(2p^(3/2)) and S(2p^(1/2))), and an N(1s)signal was observed, which indicated a displacement of approximately 60%of the thiol by the NHC;

FIG. 3E depicts representative XPS data for the treatment ofdodecanethiol-protected Au(111) surfaces with solutions of NHC-3 for at0 min and at 24 h at room temperature; the XPS spectra showed thatapproximately 45% of the S(2p) signal remained after 24 hrs and an N(1s)signal, which was not observable initially, was apparent after 24 hrs.This indicated a displacement of approximately 55% of the thiol by theNHC (the asymmetric peak was due to the presence of two electronicstates, S(2p^(3/2)) and S(2p^(1/2)));

FIG. 4 depicts various bonding modes calculated for NHC-1 on Au(111) andAu—C bond energies calculated by DFT; bonding of the NHC to the surfacevia an a-top site provided the most stable complex with a bond length inthe region expected for molecular NHC-Au complexes (note that anystabilizing effect of stacking of the benzimidazolylidene units was notfactored into these calculations which featured isolated NHCs onAu(111));

FIG. 5 depicts a high magnification image of NHC-3 on Au(111) thatshowed the presence of disorganized NHC-3 molecules, which appear assmall light regions rather than stacks as observed in FIG. 2B;

FIG. 6 depicts a low magnification image of NHC-1 on Au(111) that showeda low density of dark areas that indicated sites where the lower levelgold atoms had been removed and redistributed, likely to step edges (onestep edge was shown);

FIG. 7A depicts a low magnification image of NHC-1 on Au(111) thatshowed a low density of dark areas that indicated sites where the lowerlevel gold atoms had been removed and redistributed, likely to stepedges (one step edge was shown);

FIG. 7B depicts a low magnification image of NHC-3 on Au(111) thatshowed a high density of dark areas compared to FIG. 6; the dark areasindicated sites where the lower level gold atoms were removed andredistributed, potentially to step edges, which was possibly promoted bythe bulky size of NHC-3 compared to NHC-1; islanding was also shown bywhite spots, which were more significant for films of NHC-3 than NHC-1;

FIG. 8 depicts XPS data of films of NHC-1 on Au(111) before (tall peaks)and after (small peaks) it was exposed to 3% H₂O₂ for 24 h, and showeddecomposition;

FIG. 9 depicts XPS data of films of NHC-1 on Au(111) before and after(overlapping peaks) it was exposed to pH 2 (left) and pH 12 (right) for24 h; both cases showed stability;

FIG. 10 depicts representative XPS data (experimental and fitted) forNHC-1 on Au(111) and Au nanoparticles, the top row shows N(1s) and C(1s)on Au(111), the bottom row of spectra shows N(1s), C(1s), and S(2p) onAu nanoparticles;

FIG. 11 depicts representative XPS data (experimental and fitted) forNHC-2 on Au(111) and Au nanoparticles (see Table 1): the top row showsN(1s) and C(1s) on Au(111); the bottom row of spectra shows N(1s),C(1s), and S(2p) on Au nanoparticles;

FIG. 12 depicts representative XPS data for NHC-3 on gold surfaces andshows experimental and fitted spectra. The top row shows N(1s) and C(1s)on Au(111), the bottom row of spectra shows N(1s), C(1s), and S(2p) onAu nanoparticles;

FIG. 13 depicts representative XPS data for NHC-4 on gold surfaces (seeTable 1) and shows experimental and fitted spectra. The top row showsN(1s) and C(1s) on flat Au (111), the bottom row of spectra shows N(1s),C(1s), and S(2p) on Au nanoparticles;

FIG. 14 depicts representative XPS data for NHC-5 on gold surfaces (seeTable 1) and shows experimental and fitted spectra. The top row showsN(1s) and C(1s) on flat gold Au(111), the bottom row of spectra showsN(1s), C(1s), and S(2p) on Au nanoparticles;

FIG. 15 depicts the XPS spectroscopy results for the deposition ofNHC-3, which was obtained from a hydrogen carbonate salt of NHC-3 onAu(111) from wet methanol under air, dry methanol under air, and drymethanol under a N₂ atmosphere. These spectra were not different withinexperimental error, as shown by the overlapping data;

FIGS. 16A and 16B depict a comparison of surface plasmon resonance (SPR)scans for a NHC-16 carbene chip (see Table 1) before (16A) and after(16B) heating at 65° C. for 24 hours (4 cycles in phosphate bufferedsaline (PBS) buffer);

FIG. 17A depicts SPR data from a commercial HPA chip in PBS buffer;

FIG. 17B depicts SPR data from a NHC-16 carbene chip in PBS buffer;

FIG. 18A depicts a plot of absorbance versus time for an experimentshowing that NHC-functionalized gold samples (for example, NHC-10 goldsamples (see Table 1)) are capable of decomposing ceric ammoniumnitrate, which may be occurring by water oxidation;

FIG. 18B depicts a plot of absorbance versus time for an experimentshowing that NHC-15 gold samples (see Table 1) are capable ofdecomposing ceric ammonium nitrate, which may be occurring by wateroxidation;

FIG. 19 depicts XPS spectra of NHC-1 on Ni foil (upper panels) and on Wwire (lower panels, N is present in both cases, indicating deposition ofthe N-containing NHC;

FIG. 20 depicts XPS spectra for NHC-1-coated Pd nanoparticles;

FIG. 21A depicts XPS spectra for NHC-X deposited on Au(111) from ahydrogen carbonate precursor before (red) and after (green) treatment indecalin at 100° C. for 24 h.

FIG. 21B depicts XPS spectra for NHC-X deposited on Au(111) from ahydrogen carbonate precursor before (red) and after (green) treatment indecalin at 190° C. for 24 h

FIG. 22 depicts Scheme 1, synthesis of NHC-10.

FIG. 23 shows Table 3, which presents results of stability tests of arepresentative NHC on Au(111). For most of these XPS spectra, there is ahigh degree of overlap, suggesting no change following exposure to thestated conditions. In the C(1s) spectra on the last line, the upperspectrum is under starting conditions, and the lower spectrum is after24 hrs.

DETAILED DESCRIPTION

Definitions

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

As used in the specification and claims, the singular forms “a”, “an”and “the” include plural references unless the context clearly dictatesotherwise.

The term “comprising” as used herein will be understood to mean that thelist following is non-exhaustive and may or may not include any otheradditional suitable items, for example one or more further feature(s),component(s) and/or ingredient(s) as appropriate.

As used herein, “substituted” means having one or more substituentmoieties whose presence either facilitates or improves the desiredreaction, or does not impede the desired reaction. A “substituent” is anatom or group of bonded atoms that can be considered to have replacedone or more hydrogen atoms attached to a parent molecular entity.Examples of substituents include alkyl, alkenyl, alkynyl, aryl,aryl-halide, heteroaryl, cycloalkyl (non-aromatic ring), Si(alkyl)₃,Si(alkoxy)₃, halo, alkoxyl, amino, alkylamino, alkenylamino, amide,amidine, hydroxyl, thioether, alkylcarbonyl, alkylcarbonyloxy,arylcarbonyloxy, alkoxycarbonyloxy, aryloxycarbonyloxy, carbonate,alkoxycarbonyl, aminocarbonyl, alkylthiocarbonyl, phosphate, phosphateester, phosphonato, phosphinato, cyano, acylamino, imino, sulfhydryl,alkylthio, arylthio, thiocarboxylate, dithiocarboxylate, sulfate,sulfato, sulfonate, sulfamoyl, sulfonamide, nitro, nitrile, azido,heterocyclyl, ether, ester, silicon-containing moieties, thioester, or acombination thereof. The substituents may themselves be substituted. Forinstance, an amino substituent may itself be mono or independentlydisubstituted by further substituents defined above, such as alkyl,alkenyl, alkynyl, aryl, aryl-halide and heteroaryl cycloalkyl(non-aromatic ring).

As used herein, “aliphatic” refers to hydrocarbon moieties that arelinear, branched or cyclic, may be alkyl, alkenyl or alkynyl, and may besubstituted or unsubstituted. “Alkenyl” means a hydrocarbon moiety thatis linear, branched or cyclic and contains at least one carbon to carbondouble bond. “Alkynyl” means a hydrocarbon moiety that is linear,branched or cyclic and contains at least one carbon to carbon triplebond.

As used herein, “alkyl” refers to a linear, branched or cyclic,saturated or unsaturated hydrocarbon, which consists solely ofsingle-bonded carbon and hydrogen atoms, which can be unsubstituted oris optionally substituted with one or more substituents, for example amethyl or ethyl group. Examples of saturated straight or branched chainalkyl groups include, but are not limited to, methyl, ethyl, 1-propyl,2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl, 2-methyl-2-propyl,1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl,2-methyl-3-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl,2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl,2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl,2,2-dimethyl-1-butyl, 3,3-dimethyl-1-butyl and 2-ethyl-1-butyl, 1-heptyland 1-octyl. As used herein the term “alkyl” encompasses cyclic alkyls,or cycloalkyl groups.

The term “cycloalkyl” as used herein refers to a non-aromatic, saturatedor partially saturated, monocyclic, bicyclic or tricyclic hydrocarbonring system containing at least 3 carbon atoms. Examples of C₃-C_(n)cycloalkyl groups include, but are not limited to, cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, norbornyl,adamantyl, bicyclo[2.2.2]oct-2-enyl, and bicyclo[2.2.2]octyl.

As used herein, “alkenyl” means a hydrocarbon moiety that is linear,branched or cyclic and comprises at least one carbon to carbon doublebond which can be unsubstituted or optionally substituted with one ormore substituents. “Alkynyl” means a hydrocarbon moiety that is linear,branched or cyclic and comprises at least one carbon to carbon triplebond which can be unsubstituted or optionally substituted with one ormore substituents.

As used herein, “aryl” and/or “aromatic ring” refers to hydrocarbonsderived from benzene or a benzene derivative that are unsaturatedaromatic carbocyclic groups from 6 to 100 carbon atoms, or from whichmay or may not be a fused ring system, in some embodiments 6 to 50, inother embodiments 6 to 25, and in still other embodiments 6 to 15. Thearyls may have a single or multiple rings. The term “aryl” and/or“aromatic ring” as used herein also includes substituted aryls and/oraromatic rings. Examples include, but are not limited to, phenyl,naphthyl, xylene, phenylethane, substituted phenyl, substitutednaphthyl, substituted xylene, substituted 4-ethylphenyl and the like.

As used herein, the term “Au(111)” refers to a single crystal of gold,either alone or supported on a substrate (e.g. mica) that has aparticularly flat orientation of its atoms on the surface of thecrystal. (111) refers to a dominant arrangement of exposed surface atomsto form a 1,1,1 crystal plane (Miller indices x=y=z=+1).

As used herein, “polycrystalline gold” refers to a gold sample that hasmany small crystals of the same or different crystal structure adheredto a substrate, such as, but not limited to, a silicon wafer (thesilicon wafer may be pre-coated with a chromium or titanium layer forimproved adhesion). Such polycrystalline gold can be used forelectrochemical applications. The surface texture of polycrystallinegold can be rougher than the smooth Au(111) referred to above; however,polycrystalline gold's dominant arrangement of exposed surface atoms istypically (111). The rms-roughness (rms=root mean squared) of thepolycrystalline samples used herein was less than 2.5 nm

As used herein, “cycle” refers to an aromatic or nonaromatic monocyclic,bicyclic, or fused ring system of carbon atoms, which can be substitutedor unsubstituted. Included within the term “cycle” are cycloalkyls andaryls, as defined above.

As used herein, “heteroaryl” or “heteroaromatic” refers to an aryl(including fused aryl rings) that includes heteroatoms selected fromoxygen, nitrogen, sulfur and phosphorus. A “heteroatom” refers to anatom that is not carbon or hydrogen, such as nitrogen, oxygen, sulfur,or phosphorus. Heteroaryl or heteroaromatic groups include, for example,furanyl, thiophenyl, pyrrolyl, imidazoyl, benzamidazoyl, 1,2- or1,3-oxazolyl, 1,2- or 1,3-diazolyl, 1,2,3- or 1,2,4-triazolyl, and thelike.

As used herein, a “heterocycle” is an aromatic or nonaromatic monocyclicor bicyclic ring of carbon atoms and heteroatoms selected from oxygen,nitrogen, sulfur and phosphorus. Included within the term “heterocycle”are heteroaryls, as defined above. Also included within this term aremonocyclic and bicyclic rings that include one or more double and/ortriple bonds within the ring. Examples of 3- to 9-membered heterocyclesinclude, but are not limited to, aziridinyl, oxiranyl, thiiranyl,azirinyl, diaziridinyl, diazirinyl, oxaziridinyl, azetidinyl,azetidinonyl, oxetanyl, thietanyl, piperidinyl, piperazinyl,morpholinyl, pyrrolyl, oxazinyl, thiazinyl, diazinyl, triazinyl,tetrazinyl, imidazolyl, benzimidazolyl, tetrazolyl, indolyl,isoquinolinyl, quinolinyl, quinazolinyl, pyrrolidinyl, purinyl,isoxazolyl, benzisoxazolyl, furanyl, furazanyl, pyridinyl, oxazolyl,benzoxazolyl, thiazolyl, benzthiazolyl, thiophenyl, pyrazolyl,triazolyl, benzodiazolyl, benzotriazolyl, pyrimidinyl, isoindolyl andindazolyl.

As used herein, the term “mesityl” refers to the substituent derivedfrom mesitylene, or 1,3,5-trimethylbenzene.

As used herein, “diisopropylphenyl” is the substituent

As used herein, “NHC” refers to a N-heterocyclic carbene. Forconvenience herein, certain N-heterocyclic carbenes are referred to asNHC-1, NHC-2, etc. Structural formulae and names of these NHCs and NHCson metal are presented in Table 1.

As used herein, a “chemically derivatizable group” is any functionalgroup capable of participating in a chemical reaction, such as, but notlimited to, electrophilic/nucleophilic substitution, addition,elimination, acid/base, reduction, oxidation, radical, pericyclic,Diels-Alder, metathesis or click chemistry reactions.

As used herein, the term “unsubstituted” refers to any open valence ofan atom being occupied by hydrogen. Also, if an occupant of an openvalence position on an atom is not specified then it is hydrogen.

As used herein, a “functional group” is a specific group of atoms withina molecule that are responsible for characteristic chemical reactions.Thus functional groups are moieties within a molecule that are likely toparticipate in chemical reactions.

As used herein, “carbene” is an electronically neutral speciescomprising a carbon having two nonbonding electrons (i.e., form a lonepair), which is referred to as the “carbene carbon.” In the carbenesused in the method and materials of the present application, this carbonhaving the two nonbonding electrons is the carbon that will be bound toa metal surface and is divalent; in other words, this carbon iscovalently bonded to two substituents of any kind, and bears twononbonding electrons that may be spin-paired (singlet state), such thatthe carbon is available for formation of a dative bond.

As used herein, “N-heterocyclic carbene” refers to heterocyclic moietythat includes a carbene, as defined above, which is electronic and/orresonance stabilized, typically by the presence of one or morecarbene-adjacent heteroatoms, and/or is sterically stabilized bysubstituents adjacent to the carbene. A non-limiting example of such astabilized carbene is provided below:

As would be well appreciated by a worker skilled in the art, there aremany alternative substituents that would stabilize the carbene.Furthermore, as would be readily apparent to a worker skilled in theart, in the case of two stabilizing substituents, it is not necessaryfor the two substituents to be the same.

As used herein, a “carbene precursor” refers to a non-carbenic speciesthat, under appropriate conditions, will generate a carbene in situ,such as an N-heterocyclic carbene, as defined above, either directly, orindirectly through a transient or intermediate species.

As used herein, a “self-assembled monolayer” is a molecular assemblyformed spontaneously, from the vapour or liquid phase, onto surfaces byadsorption or chemisorption, and are organized into large, essentiallyordered domains.

As used herein, the term “composite material” refers to materials madefrom two or more constituent materials having different physical orchemical properties. Such materials may be preferred for many reasons,such as materials, which are stronger, lighter or less expensive whencompared to traditional materials. Typical composite materials aregenerally but not exclusively used for buildings, bridges and structuressuch as boat hulls, automotive and aircraft bodies, and storage tanks.Advanced examples perform on spacecraft in demanding environments.

As used herein, the term “dative bond” refers to a bond (a shared pairof electrons) forms between two atoms wherein both of the electrons thatmake up the bond came from the same atom.

As used herein, the term “uniform” when used to refer to a monolayer, asdefined above, indicates that the monolayer is generally consistent, orwithout significant variation, across substantially the entirety of thefunctionalized surface.

As used herein, the term “stability” refers to both the physical andchemical stability of the herein described carbene monolayers. “Physicalstability” refers to retention of improved physical properties ofcarbene monolayers on a timescale of their expected usefulness in thepresence of air, moisture or heat, and under the expected conditions ofapplication. This physical stability is relative to other self-assembledmonolayer-functionalized surfaces, such as thio-functionalized surfaces.“Chemical stability” refers to thermodynamic stability of the carbenemonolayers upon exposure to different chemicals or mixtures ofchemicals, including but not limited to air, oxygen, water, acid, base,oxidant, reductant, etc. It may refer to a lack of undesired chemicalreactivity exhibited by the carbene monolayers in the environment, orunder the conditions, of normal use. That is, it retains its usefulproperties on the timescale of its expected usefulness in the presenceof air, moisture or heat, and under the expected conditions ofapplication. This chemical stability may be defined relative to otherself-assembled monolayer-functionalized surfaces, such asthio-functionalized surfaces.

As used herein, the term “contaminant” or “contamination” refers to anyelemental, atomic or molecular species, or combination thereof, whosepresence impedes the desired reactions to form the herein describedcomposite materials, or impedes the desired purity, stability, orproperties of the final composite materials.

As used herein, a “metal film” refers to a metal layer that has lateraldimensions (i.e., thickness) in the range of 0.1-100 nm, oralternatively 0.1-100 μm, or alternatively >100 μm.

As used herein, “Au(NP)” refers to gold nanoparticles. As used herein, a“nanoparticle” is a plurality of metal atoms, with at least onedimension less than 100 nm, that together form a nano-scale geometricshape that is optionally multi-faceted. Properties of a metalnanoparticle typically deviate from the properties of a bulk metal.

As used herein, a “single crystal metal” refers to an entire metalsample in which a crystal lattice is continuous and unbroken to theedges of the sample.

The term “immersing” or “immersion” as used herein will be understood tomean any method of contacting a metal-containing material with carbenes,as described herein, and/or carbene precursors, as described herein, insuch a manner that a metal surface of the metal-containing material isfully or partially covered by the carbenes and/or carbene precursors.

Immersing can include, but is not limited to, dipping a metal materialinto a solution, pouring or flowing a solution over a metal surface,spraying a metal surface with a solution, or roll coating a surface.

As used herein, the term “vapour depositing” refers to deposition of afilm, coating, or self-assembled monolayer onto a surface in a vacuumenvironment, at temperatures≤0° C., or alternatively between 0-25° C.,or alternatively between 25-100° C., or alternatively ≥100° C.

As used herein, “microelectronic devices” refers to very smallelectronic designs and/or components that are made from semiconductingmaterials and manufactured on the micrometer scale, or smaller, Examplesof such devices include, but are not limited to, transistors,capacitors, inductors, resistors, diodes, insulators, conductors orcombinations thereof.

As used herein, the term “surface properties” refers to propertiesimparted to a surface as a result of being functionalized byheterocyclic carbenes, as described herein. Examples of said surfaceproperties include, but are not limited to,hydrophobicity/hydrophilicity, conductivity, electrical impedance,piezoelectricity, absorbance, radiance, fluorescence, chemical orbiochemical reactivity, or luminescence.

As used herein, the term “sensing applications” refers to systems,methods, procedures, and/or instruments that use sensors to receive andrespond to signals and/or stimuli. Examples of sensors can include, butare not limited to, optical sensors (based on, for example, absorbance,reflectance, luminescence, fluorescence, or light scattering effects);electrochemical sensors (based on, for example, voltammetric,amperometric, and potentiometric effects, chemically sensitized fieldeffect transistors, or potentiometric solid electrolyte gas sensors);electrical sensors (based on, for example, metal oxide semiconductors ororganic semiconductors); mass-sensitive sensors (based on, for example,piezoelectric or surface acoustic wave effects); magnetic sensors (basedon, for example, paramagnetic properties); thermometric sensors (basedon, for example, heat effects of a specific chemical reaction, oradsorption); radiation sensitive sensors (based on, for example,absorbance or radiation emission); biosensors (based on, for example,signal transduction, biological recognition elements, or an analytebeing sensed) [D. Buenger, F. Topuz, J. Groll, Progress in PolymerScience 37, 1678 (2012)]. Specific sensing applications can include, butare not limited to, surface plasmon resonance.

As used herein the abbreviation “XPS” is used to refer to X-rayphotoelectron spectroscopy. A typical XPS spectrum is a plot of numberof electrons detected as a function of the binding energy of detectedelectrons. Each element produces a characteristic set of XPS peaks atcharacteristic binding energy values. The peaks identify each element,and often its oxidation state, that exists on, or some 100 nm below, asurface being analyzed. XPS reveals the number of detected electrons ineach of the characteristic peaks. This number is related to the amountof an element within the sample, and it reveals whether contamination,if any, exists at the surface or in the bulk of the sample.

As used herein, the term ‘metal chip’ refers to a composite material inwhich a glass substrate has had a metal film deposited on it, comprisingappropriate connections such that it can be incorporated into acommercial surface plasmon resonance instrument.

Description

Formation of reactive, surface-bound alkylidenes has been reported [E.M. Zahidi, et al. Nature 409, 1023 (2001); G. S. Tulevski, et al.Science 309, 591 (2005)]. In one example, an NHC containing a reactivemetal alkylidene was prepared on gold, but achieved only a 20% monolayercoverage that demonstrated no stability or ordering [A. V.Zhukhovitskiy, et al. J. Am. Chem. Soc. 135, 7418 (2013)]. In anotherreport of a non-reactive NHC carbene on flat Au surfaces, an ordered NHCfilm was inferred from near edge X-ray adsorption fine structure(NEXAFS) C K-edge spectroscopy, but no stability studies were performedand no potential for derivatization illustrated [T. Weidner et al.,Aust. J. Chem. 64, 1177 (2011)]. With respect to nanoparticles, examplesof NHC-Au species have been reported, wherein stability was either poor,required rigorous conditions to achieve, or was undetermined [J.Vignolle, et al. Chem. Commun. 7230 (2009); E. C. Hurst, et al. New J.Chem. 33, 1837 (2009); R. T. W. Huang, et al. Dalton Trans. 7121(2009)].

The present application provides composite materials that comprise acarbene-functionalized metal surface. In one aspect, the compositematerial comprises a metal-containing component having a metal surfaceon which a carbene monolayer has been generated. The monolayer interactswith the metal surface via dative bonds formed between the carbenecarbon and the metal atoms. As described herein, such carbene monolayersare stable, uniform and generally free from contaminants. In certainembodiments, the carbene monolayer is a self-assembled monolayer.

In terms of uniformity, examples of the herein describedcarbene-functionalized composite materials comprise a monolayer thatexhibits uniformity across an entire treated area of a metal surface. Inexamples described herein, any variation across the monolayer that wasdetected was minimal.

In terms of stability, it has been determined that certain carbenemonolayers produced according to the methods described herein are stableto a variety of conditions. Certain of these monolayers have beendetermined to be stable since they did not degrade under ambientconditions for at least 3 months. Certain other monolayers did notdegrade under ambient conditions for at least 2 months. Furthermore,studies have been performed to demonstrate that certain monolayers arestable even with exposure for at least 24 hours to aqueous solutionshaving pHs in the range of 2-12. Similarly, exposure of compositematerials to refluxing tetrahydrofuran (“THF”), at the boiling point ofTHF (66° C.), or to boiling water, showed that certain monolayers werestable to THF and/or boiling water for at least 24 hours. Exposure ofcomposite materials to 1% H₂O₂ for 24 hours resulted in minimaldegradation (<5%) of certain carbene monolayers.

In accordance with certain embodiments, carbene monolayers of thepresent composite materials contain less than 15% contaminants, byweight, or less than 10%, or less than 5%, or less than 2%, or less than1%, or less than 0.5%. In a specific example, the carbene monolayer ofthe present composite materials comprises about 5% contaminants byweight, or less.

Carbene monolayers can be manufactured by contacting (for example, byimmersing) a metal surface with a carbene-containing liquid composition(or pure liquid carbene if possible, depending on a carbene's physicalproperties). Alternatively, certain carbene monolayers can be formedfrom carbene precursors, which form carbenes in situ.

In accordance with one embodiment, certain carbene monolayers compriseone or more carbenes of formula I

wherein:

-   -   n is an integer from 1 to 8, or from 1 to 4;    -   m is an integer from 0 to 4;    -   A is absent, an aliphatic cycle, a heterocycle, an aromatic        ring, a fused aromatic ring system, a heteroaromatic ring,        and/or a fused heteroaromatic ring system, each of which is        optionally substituted;    -   X-L-Z is absent, or    -   X is C or a heteroatom,    -   L is a divalent moiety, such as C₁-C₁₀ alkylene, C₁₀-C₂₀        alkylene, C₁-C₁₀ alkenylene, C₁₀-C₂₀ alkenylene, C₁-C₁₀        alkynylene, C₁₀-C₂₀ alkynylene, or dextran, a simple sugar,        complex sugar, carbohydrate, ether, thioether, amine, polyamine,        polyether, and/or polythioether, each of which is optionally        substituted;    -   Z is H, an aliphatic cycle, a heterocycle, an aromatic ring, a        fused aromatic ring system, a heteroaromatic ring, a fused        heteroaromatic ring system, an organometallic complex, a        transition-metal catalyst, a metal-oxide catalyst, a simple        sugar, a complex sugar, a carbohydrate, or a chemically        derivatizable group, such as —OH, azide, carboxylic acid,        carbonyl chloride, anhydride, ester, aldehyde, alcohol, amine,        halogen, epoxide, thiirane, aziridine, amino acid, nucleic acid,        alkene, alkyne, conjugated diene, thiol, or thioester, each of        which is optionally substituted;    -   each Y or Y′ is independently C or a heteroatom;    -   each R^(∘) is independently H, halogen, the substituent X-L-Z as        defined above, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, or C₁₀-C₂₀ alkynyl, C₁-C₁₀        alkoxyl, C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic moiety, aryl,        heteroaryl, ether, thioether, amine, polyamine, polyether, or        polythioether, each of which is optionally substituted; or, two        of R^(∘), together with the atoms to which they are attached,        are connected to form a cycle, or heterocycle, each of which is        optionally substituted; and    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₃-C₂₀ cyclic        aliphatic moiety, aryl, heteroaryl, ether, thiol, thioether,        amine, polyamine, polyether, polythioether, or polythiol, each        of which is optionally substituted; or, one of R¹ or R², with        one of R^(∘), together with the atoms to which they are        attached, are connected to form a cycle, or heterocycle, each of        which is optionally substituted; wherein, when A is absent or        non-aromatic, the dashed line represents an optional double        bond; and/or    -   when A is absent, each Y′ is independently bonded to R^(∘) or        X-L-Z, as defined above.

In one embodiment, the carbene is a compound of formula Ia

wherein:

-   -   m is an integer from 0 to 4;    -   each Y is independently C or a heteroatom;    -   Y² and Y³ are independently C or a heteroatom, and the dashed        line represents an optional double bond;    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₃-C₂₀ cyclic        aliphatic moiety, aryl, heteroaryl, ether, thiol, thioether,        amine, polyamine, polyether, polythioether, or polythiol, each        of which may be optionally substituted;    -   R³ and R⁴ are independently H, halogen, the substituent X-L-Z as        defined for Formula I, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀        alkenyl, C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl,        C₃-C₂₀ cyclic aliphatic moiety, C₁-C₁₀ alkoxyl, C₁₀-C₂₀ alkoxyl,        C₃-C₂₀ cyclic aliphatic moiety, aryl, heteroaryl, ether,        thioether, amine, polyamine, polyether, or polythioether, each        of which is optionally substituted; or, any one of R³ or R⁴,        with any one of R¹ or R², together with the atoms to which they        are attached, are connected to form a cycle, or heterocycle,        each of which is optionally substituted.

In certain embodiments, R¹ and R² are independently methyl, ethyl,propyl, butyl, isopropyl, phenyl, mesityl, or diisopropylphenyl, each ofwhich may be optionally substituted.

In an alternative embodiment, certain monolayers are formed from acarbene precursor, such that a carbene is formed in situ in preparationof carbene monolayers. In one example of this embodiment, the carbeneprecursor is contacted with a metal surface (for example, by immersionand/or thermal decomposition) to form a carbene monolayer. This processis suitable, for example, when the carbene precursor is a compound offormula II

wherein:

-   -   n is an integer from 1 to 8, or from 1 to 4;    -   m is an integer from 0 to 4;    -   B is a counter ion that optionally acts as a base;    -   A is absent, an aliphatic cycle, a heterocycle, an aromatic        ring, a fused aromatic ring system, a heteroaromatic ring,        and/or a fused heteroaromatic ring system, each of which is        optionally substituted;    -   X-L-Z is absent, or    -   X is C or a heteroatom,    -   L is a divalent moiety, such as C₁-C₁₀ alkylene, C₁₀-C₂₀        alkylene, C₁-C₁₀ alkenylene, C₁₀-C₂₀ alkenylene, C₁-C₁₀        alkynylene, C₁₀-C₂₀ alkynylene, or dextran, a simple sugar,        complex sugar, carbohydrate, ether, thioether, amine, polyamine,        polyether, and/or polythioether, each of which is optionally        substituted;    -   Z is H, an aliphatic cycle, a heterocycle, an aromatic ring, a        fused aromatic ring system, a heteroaromatic ring, a fused        heteroaromatic ring system, an organometallic complex, a        transition-metal catalyst, a metal-oxide catalyst, a simple        sugar, a complex sugar, a carbohydrate, or a chemically        derivatizable group, such as —OH, azide, carboxylic acid,        carbonyl chloride, anhydride, ester, aldehyde, alcohol, amine,        halogen, epoxide, thiirane, aziridine, amino acid, nucleic acid,        alkene, alkyne, conjugated diene, thiol, or thioester, each of        which is optionally substituted;    -   each Y or Y′ is independently C or a heteroatom;    -   each R^(∘) is independently H, halogen, the substituent X-L-Z as        defined above, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₁-C₁₀ alkoxyl,        C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic moiety, aryl,        heteroaryl, ether, thioether, amine, polyamine, polyether, or        polythioether, each of which is optionally substituted; or, two        of R^(∘), together with the atoms to which they are attached,        are connected to form a cycle, or heterocycle, each of which is        optionally substituted; and    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₃-C₂₀ cyclic        aliphatic moiety, aryl, heteroaryl, ether, thiol, thioether,        amine, polyamine, polyether, polythioether, or polythiol, each        of which is optionally substituted; or, one of R¹ or R², with        one of R^(∘), together with the atoms to which they are        attached, are connected to form a cycle, or heterocycle, each of        which is optionally substituted; wherein, when A is absent or        non-aromatic, the dashed line represents an optional double        bond; and/or    -   when A is absent, each Y′ is independently bonded to R^(∘) or        X-L-Z, as defined above; or, the carbene precursor is a compound        of formula IIa

wherein:

-   -   m is an integer from 0 to 4;    -   B is a counter ion that optionally acts as a base;    -   each Y is independently C or a heteroatom;    -   Y² and Y³ are independently C or a heteroatom, and the dashed        line is an optional double bond;    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl), cycloalkyl,        aryl, heteroaryl, ether, thiol, thioether, amine, polyamine,        polyether, polythioether, or polythiol, each of which is        optionally substituted;    -   R³ and R⁴ are independently H, halogen, the substituent X-L-Z as        defined for Formula II, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀        alkenyl, C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl,        C₁-C₁₀ alkoxyl, C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic, aryl,        heteroaryl, ether, thioether, amine, polyamine, polyether, or        polythioether, each of which is optionally substituted; or, any        one of R³ or R⁴, with any one of R¹ or R², together with the        atoms to which they are attached, are connected to form a cycle,        or heterocycle, each of which is optionally substituted;    -   or, the carbene precursor is a compound of formula III:

wherein:

-   -   n is an integer from 1 to 4, or alternatively 1 to 8;    -   m is an integer from 0 to 4;    -   G is a perhalogenated alkyl, perhalogenated alkenyl,        perhalogenated alkynyl, a perhalogenated aryl, or OR′, wherein        R′ is an aliphatic group, for example, an alkyl group.    -   A is absent, an aliphatic cycle, a heterocycle, an aromatic        ring, a fused aromatic ring system, a heteroaromatic ring,        and/or a fused heteroaromatic ring system, each of which is        optionally substituted;    -   X-L-Z is absent, or    -   X is C or a heteroatom,    -   L is a divalent moiety, such as C₁-C₁₀ alkylene, C₁₀-C₂₀        alkylene, C₁-C₁₀ alkenylene, C₁₀-C₂₀ alkenylene, C₁-C₁₀        alkynylene, C₁₀-C₂₀ alkynylene, or dextran, a simple sugar,        complex sugar, carbohydrate, ether, thioether, amine, polyamine,        polyether, and/or polythioether, each of which is optionally        substituted;    -   Z is H, an aliphatic cycle, a heterocycle, an aromatic ring, a        fused aromatic ring system, a heteroaromatic ring, a fused        heteroaromatic ring system, an organometallic complex, a        transition-metal catalyst, a metal-oxide catalyst, a simple        sugar, a complex sugar, a carbohydrate, or a chemically        derivatizable group, such as —OH, azide, carboxylic acid,        carbonyl chloride, anhydride, ester, aldehyde, alcohol, amine,        halogen, epoxide, thiirane, aziridine, amino acid, nucleic acid,        alkene, alkyne, conjugated diene, thiol, alkyl thiol, or        thioester, each of which is optionally substituted;    -   each Y or Y′ is independently C or a heteroatom;    -   each R^(∘) is independently H, halogen, the substituent X-L-Z as        defined above, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, or C₁₀-C₂₀ alkynyl, C₁-C₁₀        alkoxyl, C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic moiety, aryl,        heteroaryl, ether, thioether, amine, polyamine, polyether, or        polythioether, each of which is optionally substituted; or, two        of R^(∘), together with the atoms to which they are attached,        are connected to form a cycle, or heterocycle, each of which is        optionally substituted; and    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, branched C₁-C₁₀        alkyl, C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, or C₁₀-C₂₀ alkynyl),        C₃-C₂₀ cyclic aliphatic moiety, aryl, heteroaryl, ether, thiol,        thioether, amine, polyamine, polyether, polythioether, or        polythiol, each of which is optionally substituted; or, one of        R¹ or R², with one of R^(∘), together with the atoms to which        they are attached, are connected to form a cycle, or        heterocycle, each of which is optionally substituted;    -   wherein, when A is absent or non-aromatic, the dashed line        represents an optional double bond; and/or    -   when A is absent, each Y′ is independently bonded to R^(∘) or        X-L-Z, as defined above; or, the carbene precursor is a compound        of formula IIIa:

wherein:

-   -   m is an integer from 0 to 4;    -   G is a perhalogenated alkyl, perhalogenated alkenyl,        perhalogenated alkynyl, a perhalogenated aryl, or OR′, wherein        R′ is an aliphatic group, for example, an alkyl group.    -   each Y or Y′ is independently C or a heteroatom;    -   Y² and Y³ are independently C or a heteroatom, and the dashed        line represents an optional double bond;    -   R¹ and R² are independently absent, at least one lone pair of        electrons, H, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl,        C₁₀-C₂₀ alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, cycloalkyl,        aryl, heteroaryl, ether, thiol, thioether, amine, polyamine,        polyether, polythioether, or polythiol, each of which may be        optionally substituted;    -   R³ and R⁴ are independently H, halogen, the substituent X-L-Z as        defined for Formula III, C₁-C₁₀ alkyl, C₁₀-C₂₀ alkyl, branched        C₁-C₁₀ alkyl, branched C₁₀-C₂₀ alkyl, C₁-C₁₀ alkenyl, C₁₀-C₂₀        alkenyl, C₁-C₁₀ alkynyl, C₁₀-C₂₀ alkynyl, C₁-C₁₀ alkoxyl,        C₁₀-C₂₀ alkoxyl, C₃-C₂₀ cyclic aliphatic, aryl, heteroaryl,        ether, thioether, amine, polyamine, polyether, or polythioether,        each of which is optionally substituted; or, any one of R³ or        R⁴, with any one of R¹ or R², together with the atoms to which        they are attached, are connected to form a cycle, or        heterocycle, each of which is optionally substituted.

In one example, the carbene precursor is as defined above, wherein R¹and R² are independently methyl, ethyl, propyl, butyl, isopropyl,phenyl, mesityl, or diisopropylphenyl, each of which may be optionallysubstituted.

In an alternative embodiment, certain carbene monolayers are prepared byvapour depositing a carbene, or carbene precursor, as defined above, ona metal surface.

Carbene-functionalized composite materials are prepared from a materialthat comprises a metal surface. The material can be a solid metal, ametal film, a metal sheet or metal nanoparticles (pure or mixed metal).By way of further example, the metal surface can be on a metal film orlayer on a support material, a surface of a metal particle ornanoparticle, a surface of a solid metal or a surface of a singlecrystal metal. A metal surface can comprise an alloy such as steel(including stainless steel), brass, bronze, tungsten carbide, calciumcarbide, or any combination thereof. Alternatively, or in combination, ametal surface can comprise Fe, Rh, Ir, Ni, Pd, Pt, Cr, Cu, Ag, Au, W, orany combination thereof. In an example, in which a metal surface is afilm or a layer on a solid support, the solid support can comprise, forexample, mica, alumina, silica, titania, silicon, glass or indium tinoxide. Gold is used as an example metal in many of the studies describedherein. It was chosen for surface studies since it does not react withO₂ to form an oxide and since it can be obtained as single crystals withclean surfaces. Other studies herein use palladium, copper, nickel andtungsten. Gold, palladium, nickel, copper and tungsten were used merelyas examples of metals that can be coated with carbenes and are not meantto be limiting.

In certain embodiments, carbene-functionalized composite materials areprepared as described herein, using carbenes or carbene precursors thatcomprise one or more chemically derivatizable groups. Compositematerials prepared using such carbenes or carbene precursors comprise acarbene monolayer that can be chemically modified by treatment of thechemically derivatizable groups, for example, to obtain desiredcomposite material properties.

Carbene-functionalized composite materials of the present applicationare useful for, or can be configured for use in, various applications.In general, the process and materials described herein may be used tomodify the properties of a metal surface of a material. For example, itmay be desirable to modify a metal surface of a material by changing itssurface properties (e.g., its surface wettability), by protecting themetal surface, by chemically activating or deactivating the metalsurface to make it reactive or unreactive to a selected reagent orcombination of reagents, or by displacing existing chemical groups ormoieties from the metal surface (e.g., thio-containing compounds orgroups). More specifically, the presently described process andmaterials can be used in the following, non-limiting, examples ofapplications:

-   -   making nano-patterns on semi-conducting surfaces;    -   fabricating electronic or microelectronic devices;    -   drug delivery;    -   electrochemically detecting molecules including biomolecules        such as DNA, proteins, lipids or glucose, via, for example,        non-specific adsorption;    -   surface plasmon resonance for detecting molecules, or        specifically biomolecules such as DNA, proteins, lipids or        glucose via, for example, non-specific adsorption;    -   making electrochemical sensors;    -   sensing applications;    -   colorimetric analysis of molecules, such as biomolecules; or    -   protecting metal surfaces from, for example, oxidation or        corrosion.

Described herein is a new method for functionalizing metal surfaces byforming a metal-carbon dative bond with carbenes, such as, but notlimited to, N-heterocyclic carbene, which results in stable monolayerfilms that are chemically derivatizable. Although not wishing to bebound by theory, it has been suggested that the carbene-carbon'sselection of a-top gold atoms means the resultant functionalizedsurfaces are characterized by a novel bonding mode and ligand class, andare more stable in air, solvents, and higher temperatures than thecurrent metal-thiol systems (for example, in the gas phase Au—C is 557kJ/mol, and Au—S is 295 kJ/mol).

One important factor to many technological applications, such asnano-patterned semiconducting surfaces, drug delivery, and biomoleculedetection, is surface functionalization, wherein a single layer ofmolecules is chemically bound to a surface to change its physical andchemical properties. Thus, the herein described method of surfacefunctionalization using modified carbenes was developed, which has beendemonstrated on gold (FIGS. 1-4), palladium (FIG. 20), copper, tungstenand nickel (FIG. 19) and, may be applied to silver, palladium, and othermetals. Various metal surfaces have been amenable to thisfunctionalization, such as bulk metal, thin films, atomically orderedsurfaces, and metal nanoparticles. Through the herein described methodof surface functionalization, any functional group could be grafted to ametal surface to form a stable, uniform, single-molecular layers (alsoknown as a self-assembled monolayer).

One method to functionalize gold, and to a lesser degree silver andcopper, is to expose them to a solution of an alkanethiol [C. D. Bain,E. D. Troughton, Y.-T. Tao, J. Evall, G. M. Whitesides, R. G. Nuzzo, J.Am. Chem. Soc. 111, 321 (1989)]. The alkanethiol spontaneously forms acontinuous, ordered, single-layer of the alkanethiol at the surface,attached to the metal via a metal-sulfur bond, resulting in aself-assembled monolayer (SAM). Alternatively, the alkanethiol may bedeposited electrochemically on the surface. One described variant ofthis method is one in which either graphite or gold surfaces may befunctionalized by electrochemical deposition of a diazonium salt,wherein a Au—C bond is formed [J. Pinson, et al. Chem. Soc. Rev. 34,429, (2005)]. These functionalized surface films tend to be less orderedand less continuous than for alkanethiols, and tend to be more than onemolecular layer thick. Reports make no comment on the stability of thesefilms. Functionalization of gold nanoparticles via a Au—C bond usingdiazonium salts is limited by formation of a radical intermediate thatreacts to form disordered and multilayer molecular films [L. Laurentius,et al. ACS Nano. 5, 4219 (2011)].

Other workers have successfully functionalized alkylidene species tomolybdenum carbide (MoC) or ruthenium (Ru) surfaces [G. S. Tulevski, etal. Science 309, 591 (2005); G. A. Ozin, et al. Nanochemistry: AChemical Approach to Nanomaterials, RSC Publishing, Cambridge, UK,(2005)]. In these cases, linkage was via a metal-carbon double bond.

Other technologies can be used to form SAMs on semiconductor, glass ormetal oxide surfaces [G. S. Tulevski, et al. Science 309, 591 (2005)].In some cases, a siloxane linkage (C—Si—O) is formed. However, suchtechnologies are ineffective for functionalizing pure metal surfaces.Functionalizing pure metal surfaces has some advantages: it allows forbinding of a ligand (or analyte) to be detected electrochemically. Goldis interesting because it is a biocompatible and relatively inert metal.

A limitation of using alkanethiols is that they can be unstable; theyare expected to desorb from a bulk Au or thin Au film surfaces attemperatures of 70° C. or higher. They are particularly unstable inhydrophobic solvents at higher temperatures [C. D. Bain, et al. J. Am.Chem. Soc. 111, 321 (1989)], and they are known to begin decomposing inair at room temperature within a week. They can also be susceptible toexchange with amines or other thiol. This can pose a particularchallenge if amino acid or protein species are to be bound to thesurface and in in vivo biological systems where thiols abound. Thiolmonolayers have been shown to begin decomposing by oxidation in air atroom temperature after as little as 1-2 weeks [C. Vericat, et al. J.Phys. Condens. Matter 20, 184004 (2008); Y. Li, et al. J. Am. Chem.Soc., 114, 2428 (1992); M. H. Schoenfisch, et al. J. Am. Chem. Soc. 120,4501 (1998); J. B. Schlenoff, et al. J. Am. Chem. Soc. 117, 12528(1995)]. This limits the stability of such surfaces and thus the abilityof thiol monolayers to protect surfaces. Furthermore, an Au—S bond canbe a poor conductor where compared to certain Au—C bondingconfigurations [J. M. Seminario, et al. J. Am. Chem. Soc. 123, 5616(2001)]; coupling a hydrocarbon-based compound to a metal via acarbon-metal bond, particularly one adjacent to a delocalised electronicsystem as is exhibited by the carbenes described herein, could be usefulin maintaining a high conductivity at any metal/organic interface usedin an electronic device.

In general, alkylidenes form stable monolayers on substrates that aregood conductors (non-limiting examples include Ru or MoC). However,unlike gold, Ru and MoC are not materials that are routinelyincorporated as part of the microelectronic fabrication industry. It ispossible that alkylidenes will not form stable monolayers on Au, ascompared to those formed with Ru or MoC, and thus use of alkylidenes maynot be as straightforward as with N-heterocyclic carbenes, as describedherein.

On MoC, the Mo═C double bond appears to be stable up to approximately600° C. in vacuum. Stability of alkylidene monolayers on Ru underambient conditions is similar to the gold carbene monolayers describedherein. Alkylidenes are stable at room temperature in non-aqueoussolvents. However, the gold carbene monolayers described herein arestable at higher temperatures in such solvents, and are also stable inboiling water for at least 24 hours. These are conditions that a SAMmust be able to withstand if it were to act as a structural support forcatalytic reactions on a surface. Alkylidene monolayers are primarilyutilized as catalytic platforms for methathesis reactions, in which thecarbon-meal bond itself takes part in the reaction. The herein describedcarbene monolayers on gold, by contrast, have been specifically designedto be unreactive; they can therefore act as a structural platform tosupport other functional groups that will be able to modify variousproperties of the metal surface, including its catalytic activity, andthus should support a much wider range of applications. In addition, thecarbenes discussed herein are much more general in terms of the type ofmetal they bond to. The herein described carbene monolayers can beremoved by various means. For example, to remove the herein describedcarbenes from a surface, they can be physically abraded, together withsome or all of the underlying metal film, or exposed to strong oxidizingconditions such as, but not limited to, exposure to 3% H₂O₂ for 24hours. Further, it has been shown that the herein described carbenes canbe removed with heat (˜190° C.) and decalin, or the like, as solvent.

With the method of surface functionalization described herein, it hasbeen demonstrated that Au surfaces or nanoparticles can befunctionalized by SAM formation through the displacement of surfacethioethers. The resultant carbene-functionalized surface was found to bestable against incorporation of thiols or thioethers, as determined byXPS analyses that show no S on the surface (FIG. 1A-D). It was alsodemonstrated that Au surfaces or nanoparticles could be functionalizedby displacement of surface thiols; some thiols, remained, however.

The stability of these carbene SAM-functionalized metal surfaces hasbeen demonstrated. Carbenes bound to gold surfaces were resistant toexchange by sulfur ligands, indicating that the Au—C bond is more stablethan the Au—S bond. The nanoparticles were stable for at least 15 weeksunder ambient conditions, and surfaces were stable in non-aqueoussolvents such as THF at temperatures of up to 70° C. for 24 hours.Surfaces modified by carbenes were stable after boiling in water in airfor 24 hrs, they were stable to pH 2 and pH 12 at room temperature and100° C., and, 85% of the film has been shown to survive overnight in 1%hydrogen peroxide (FIGS. 8-9).

The ability of these carbene monolayer-functionalized metal surfaces toadjust surface properties has been demonstrated by modifying the carbenebackbone to impart hydrophobic or hydrophilic properties to a surface(FIG. 3). The ability to modify said carbene monolayers and affectsurface properties can be relevant to sensing applications.

NHCs necessary to affect this surface functionalization are stablerelative to other carbenes, which decompose, often violently, undernon-cryogenic conditions or when exposed to a variety of simplechemicals. Comparatively, NHCs are stable enough to be bottled,crystallized, and even distilled. It has been shown that NHCs can bestored in a regular freezer, under nitrogen without any evidence ofdecomposition for upwards of four years.

Additionally, precursors of the herein described NHCs are stable underambient conditions; conversion to the desired carbenes typicallyrequires treatment with base and filtration. Resulting solutions can beused directly in the formation of self-assembled monolayers on metal.Monolayer formation has been shown to occur in just a few hours or lessat room temperature by immersing the gold substrate in a solution of thedesired carbene; thus, preparation of a stable monolayer on gold can besimple and readily accomplished.

While there have been a few studies of reactive carbenes (alkylidenes)on metal surfaces, which bind via a reactive metal-carbon double bond,[E. M. Zahidi, et al., Nature 409, 1023 (2001); G. S. Tulevski, et al.,Science 309(5734), 591-594 (2005)] there have been few reports on theuse of stable, bottleable NHC-type carbenes for the formation of singlebonds to metal surfaces resulting in non-reactive surfaces.

In terms of NHC-type carbenes, there are two reports [T. Weidner et al.,Aust. J. Chem. 64, 1177 (2011); A. V. Zhukhovitskiy, et al. J. Am. Chem.Soc. 135, 7418 (2013)]. In the more recent report, a NHC containing anappended reactive metal alkylidene was prepared on gold; however, only a20% monolayer coverage was achieved and no stability or ordering wasdemonstrated. In the only other report of NHCs on flat Au surfaces, anordered NHC film was inferred from NEXAFS C K-edge spectroscopy, but nostability studies were performed and no potential for derivatizationillustrated. With respect to nanoparticles, examples of NHC-Au specieshave been described [J. Vignolle, et al. Chem. Commun. 7230 (2009); E.C. Hurst, et al. New J. Chem. 33, 1837 (2009); R. T. W. Huang, et al.Dalton Trans. 7121 (2009)]. In these reports, the stability of thefunctionalized surface was either determined to be low, to require agingvia multiple dissolution/precipitation cycles, or was not largelyassessed.

There are many applications envisioned for the herein describedcarbene-functionalized metal surfaces. One application in which SAMs onAu are used routinely on a commercial basis is surface plasmon resonance(SPR). In SPR, a thin Au film functionalized with an appropriate proteinor antibody is used to detect biomolecules in solution: as analytes fromsolution are adsorbed onto a film, reflectance of the film changes, andthe quantity of analyte adsorbed can be detected optically. Currently,thiol SAMs are used to functionalize Au films, which are subject todegradation. An N-heterocyclic carbene monolayer could substitute forthe thiol, in principle forming a more stable film with a longerdetector lifetime. Further, SPR detector chips have to be stored in afreezer under N₂ to preserve functionality, and have a shelf life of6-12 months. Substitution of thiol SAMs with NHC SAMs can providedetectors that can be stored under ambient conditions, with longer shelflives. It has been demonstrated, using NHC-16 on a Au film, that theNHC-functionalized metal surface will adsorb a lipid overlayer film, asmeasured using SPR, with stability and reproducibility greater than thatof a commercially available alkanethiol-based Au film (Table 5 and FIGS.15 and 16).

Functionalized gold nanoparticles have also demonstrated promise in thedetection or analysis of molecules via colorimetric analysis [J. Liu, etal. Agnew. Chem., Int. Ed. 45, 90, (2006)]. Nanoparticles arefunctionalised with a DNA aptamer, which is designed to bind an analyte.Once bound, the nanoparticles aggregate, changing colour.

Opportunities exist in other applications that are less commerciallydeveloped, such as the use of functionalized Au nanoparticles for cancertreatment [B. Kang, et al. J. Am. Chem. Soc. 132, 1517, (2010)]. In thiscase, use of a more stable N-heterocyclic carbene functionalised surfacemay prolong shelf life of any drug compound formed. Coupling organicmolecules to metals is also an important step in building novelelectronic devices. The ability to form stable patterns on a surfacecould potentially be an important step in bottom-up approaches for thesemiconductor industry [R. K. Smith, et al. Prog. Surf. Sci. 75, 1,(2004); Rahul Bhure, et al. ACS Symposium Series, Vol. 1054 Chapter 4(2010); A. Kumar, et al. Langmuir 10, 1498 (1994)]. Further, the hereindescribed carbene SAMs can be used to aid in selectively functionalizingmaterials containing both metal and non-metal surfaces. For example, thecarbene-monolayer can be applied as a nano-scale protecting group,coating the metal surface to allow selective etching orfunctionalization of the non-metal surface, after which the carbene SAMcan be selectively removed.

Envisioned applications include the use of carbene-functionalizedsurfaces in the field of supported catalysis, includingelectrocatalysis, wherein the carbene SAM on the metal surface is itselffurther functionalized with active metal catalysts. It has beendemonstrated using, for example, NHC-10 on a gold film, that thiscompound will successfully catalyze the reproducible and repeatabledecomposition of ceric ammonium nitrate in aqueous acidic solution,which may occur through water oxidation (FIG. 18A). In furtherembodiments, the carbene-functionalized surfaces can be employed toimmobilized or bind catalysts useful for catalytic reactions, such as inH₂ production or CO oxidation. As would be readily within the skill of aworker skilled in the art, selection of the appropriate catalyst, suchas a transition metal catalyst, will be based on the type of reaction tobe catalyzed.

In a further embodiment, the composite materials described herein areelectrochemically stable (C. M. Crudden, et al. Nature Chem. 6, 409-414(2014), which is incorporated herein in its entirety).

To gain a better understanding of the invention described herein, thefollowing working examples are set forth. It should be understood thatthese examples are for illustrative purposes only. Therefore, theyshould not limit the scope of this invention in any way. Examples ofseveral NHCs having the above general formulas are provided herein.Stability test data is summarized in Table 3 of FIG. 23.Characterization data for NHC-coated Palladium is presented in Table 4.Synthetic information and characterization are provided in the WorkingExamples. A comparison of HPA sensor chips and NHC sensor chips isprovided in Tables 5A and 5B. In addition, details of successfulapplication of NHCs on metal surfaces are provided. For moreinformation, see Crudden, C. M., Horton, J. H. et al. Nature Chem. 6(5):409-414 (2014) including supplementary material.

WORKING EXAMPLES

Synthesis and deposition of carbenes were carried out in a nitrogenatmosphere in a glovebox (M. Braun) with oxygen and water levels≤2 ppm.Solvents were purified on a PureSolv Solvent Purification system,distilled, degassed and stored over 4 Å molecular sieves prior to use.Reactants were obtained from Aldrich Chemical Company (Oakville,Ontario, Canada) unless otherwise specified. Hydrogen tetrachloroaurate[HAuCl₄] was synthesized by the oxidation of gold metal throughdissolution in aqua regia. Aqua regia was prepared as a mixture ofconcentrated nitric and hydrochloric acid (1:3 ratio v/v). Gold wire wasdissolved in an appropriate volume of aqua regia solution such that nosolid remained. Careful evaporation of the solution after 24 hoursyielded chloroauric acid tetrahydrate as a yellow solid. Au(111) waspurchased from Georg Albert PVD—Beschichtungen of Hauptstr, Germany.Polycrystalline gold refers to gold that was adhered to a silicon wafer(available from Western nanofabrication facility, University of WesternOntario, London, ON, Canada). The wafer was precoated with a chromium ortitanium layer for improved adhesion.

¹H and ¹³C{¹H} Nuclear Magnetic Resonance (NMR) spectra were recorded ona BrukerAvance-400 or 500 MHz spectrometer (available from Milton,Ontario, Canada). Chemical shifts were reported in delta (δ) units,expressed in parts per million (ppm) downfield from tetramethylsilaneusing residual protonated solvent as an internal standard (C₆D₆, 7.15ppm; CDCl₃, 7.24, CD₂Cl₂, 5.32 ppm). Chemical shifts were reported asabove using solvent as an internal standard (C₆D₆, 128.0 ppm; CDCl₃,77.23, CD₂Cl₂, 53.8 ppm). All 2D spectra (gs-COSY, gs-HSQC, gs-HMBC)were acquired in phase-sensitive mode. All data were acquired,processed, and displayed using Bruker XWinNMR and ACD Labs software anda standard pulse-sequence library. All measurements were carried out at298 K unless otherwise stated.

Mass-spectrometry was carried out using a Micromass Platform LCZ 4000system (available from Waters, Mississauga, Ontario, Canada). Elementalanalyses were performed using Flash 2000 CHNS-O analyzer (available fromThermo Scientific). XPS measurements were performed using a ThermoMicrolab 310F ultrahigh vacuum (UHV) surface analysis instrument(available from ThermoScientific) using Mg Kα X-rays (1253.6 eV) at 15kV anode potential and 20 mA emission current with a surface/detectortake off angle of 75°. The binding energy of all spectra was calibratedto the Au 4f line at 84.0 eV. A Shirley background subtraction algorithmwas used as the background subtraction method for all peaks. The Powellpeak-fitting algorithm was used, with peak areas normalized betweendifferent elements using the relative XPS sensitivity factors ofScofield [Scofield, J. H. Hartree-Slater subshell photoionizationcross-sections at 1254 and 1487 eV. J. Electron Spectrosc. Relat.Phenom. 8, 129-137 (1976)]. In cases where absolute peak intensities fora single element were compared between different samples, a standardsample size and orientation with respect to X-ray source and detectorwithin the analysis chamber were used. Calibration using Au thiol SAMsof known surface concentration showed that peak areas were reproduciblewithin ±5% between sample runs.

Scanning tunnelling microscope (STM) measurements were performed inultra-high vacuum at room temperature using a custom Pan-style STM.Mechanically-formed platinum-iridium tips were used for all experiments.GXSM [Zahl, P., et al. J. Vac. Sci. Tech. B 28, C4E39 (2010)] was usedas control software using the Signal Ranger A810 DSP and Nanonis HVA4high-voltage amplifier.

Example 1. Synthesis of N-Heterocyclic Carbenes Example 1A. Synthesis of1,3-Dihydro-1,3-bisisopropyl-2H-benzimidazol-2-ylidene, (“IPrBenz” or“NHC-1”)

1,3-Diisopropyl-1H-benzo[d]imidazole-3-ium iodide (317 mg, 0.908 mmol)[Huynh, H. V., et al. Organometallics 25, 3267-3274 (2006)] wasdissolved in 10 mL of anhydrous THF in a glove box. A solution of KOtBu(108 mg, 0.908 mmol) in THE (20 mL) was added dropwise over an hour. Thereaction was stirred for an additional hour. The THF was then evaporatedunder vacuum, and the resulting residue was dissolved in toluene andfiltered through Celite®. Evaporation of the filtrate gave the desiredfree carbene as a yellow oil in 68% yield. ¹H NMR (C₆D₆) δ (ppm):7.3-7.2 (br, 4H, PhH), 4.52 (sept, J_(HH)=6.6 Hz, 2H, CH—(CH₃)₃), 1.63(d, J_(HH)=6.65 Hz, 12H, CH₃).

Example 1B. Synthesis of2,4-Dihydro-2,4,5-triphenyl-3H-1,2,4-triazol-3-ylidene (“Enders Carbene”or “NHC-2”);1,3-dihydro-1,3-bis(2,4,6-trimethylphenyl)-2H-imidazol-2-ylidene (“IMes”or NHC-3); 1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene (“SIMes”or “NHC-4”); and1,3-dihydro-1,3-bis(2,6-diisopropylphenyl)-2H-imidazol-2-ylidene (“IPr”or NHC-5)

These carbenes were prepared using a similar method as described inEnders, D., et al. Angew. Chem. Int. Ed. 34, 1021 (1995); Arduengo, A.J., et al. J. Am. Chem. Soc. 114, 5530 (1992); Arduengo, A. J., et al.Tetrahedron 55, 14523-14534(1999); and Jafarpour, J., et al. J.Organomet. Chem. 606, 49-54 (2000). Structural formulae are shown inTable 1. As a person of skill in the art will recognize, structuralformula of free NHCs can be deduced by looking at a structural formulaof an NHC on gold, and changing the bond that links the carbene carbonto the gold surface into the absence of a bond, with a lone pair ofelectrons on the carbene carbon.

Example 1C. Five Step Synthesis of1,3-diisopropyl-5-(12-(azido)dodecyloxy)-1H-benzo[d]imidazole-2-ylidene,(“NHC-6”) (i) Synthesis of 4-(12-Bromododecyloxy)-2-nitroaniline

To a solution of 4-amino-3-nitrophenol (616 mg, 4 mmol) and1,12-dibromo-dodecane (2.624 g, 8 mmol) in anhydrous acetonitrile (40mL), potassium carbonate (552 mg, 4 mmol) was added. The mixture wasstirred at 80° C. for 8 h under argon. The solvent was then evaporatedand the crude product was separated by flash-chromatography usinghexane-ethyl acetate gradient mixtures. Yield: 1.130 g (70%). Anal.Calc. for C₁₈H₂₉BrN₂O₃: C, 53.87; H, 7.28; N, 6.98. Found: C, 53.31; H,7.12; N, 7.10. ¹H NMR (CDCl₃) δ (ppm): 7.54 (d, 1H, J_(HH)=2.7 Hz, ArH),7.07 (dd, 1H, J_(HH)=9.0 Hz, J_(HH)=2.7 Hz, ArH), 6.76 (d, 1H,J_(HH)=9.1 Hz, ArH), 5.88 (s, 2H, NH₂), 3.92 (t, 2H, J_(HH)=6.5 Hz,0-CH₂), 3.41 (t, 2H, J_(HH)=6.8 Hz, Br—CH₂), 1.86 (t, 2H, J_(HH)=7.3 Hz,J_(HH)=7.0 Hz), 1.77 (tt, 2H, J_(HH)=7.6 Hz, J_(HH)=6.6 Hz), 1.43 (m,br, 4H), 1.29 (m, br, 12H). ¹³C{¹H} NMR (CDCl₃) S (ppm): 150.27 (s,C_(q), CO—CH₂), 139.74 (s, C_(q), C—NO₂), 131.54 (s, C_(q), C—NH₂),127.06 (s, Ar), 119.96 (s, Ar), 107.11 (s, Ar), 68.76 (s, CH₂—O), 34.04(s), 32.80 (s), 29.47 (m), 29.39 (s), 29.30 (s), 29.07 (s), 28.72 (s),28.14 (s), 25.94 (s).

(ii) Synthesis of 5-(12-Bromododecyloxy)-1H-benzo[d]imidazole

This synthetic procedure was adapted from Hanan, E. J., et al. Synlett,2759-2764 (2010). Formic acid (25 mL) was added to a mixture of4-(12-bromododecyloxy)-2-nitroaniline (2.005 g, 5 mmol), iron powder(2.790 g, 50 mmol), and ammonium chloride (2.670 g, 50 mmol) inisopropanol (35 mL). The resulting mixture was stirred at 80° C. for 3 hunder argon, then cooled to room temperature and filtered. A resultantsolid material was washed with isopropanol (3×5 mL). A resultantfiltrate was evaporated to dryness and a residue was partitioned betweensaturated NaHCO₃ (20 mL) and CHCl₃ (20 mL). The water phase wasadditionally extracted with chloroform (3×20 mL). Combined non-aqueouslayers were evaporated in vacuo to give a product that was used in thenext step without further purification. Yield 1.735 g (91%). Anal. Calc.for C₁₉H₂₉BrN₂O: C, 59.84; H, 7.66; N, 7.35. Found: C, 58.07; H, 7.85;N, 7.34. ES-MS (m/z) for C₁₉H₂₉N₂OBr: 380.1475, Calc.: 380.1463. ¹H NMR(DMSO-d₆) δ (ppm): 8.14 (s, 1H, NH), 8.08 (s, 1H, N—CH═N), 7.44 (d, 1H,J_(HH)=8.8 Hz, ArH), 7.04 (s, 1H, ArH), 6.79 (d, 1H, J_(HH)=8.8 Hz,ArH), 3.95 (t, 2H, J_(HH)=6.3 Hz, 0-CH₂), 3.50 (t, 2H, J_(HH)=6.6 Hz,Br—CH₂), 1.77 (m, 2H), 1.71 (m, 2H), 1.42-1.33 (m, br, 4H), 1.25 (m, br,12H). ¹³C{¹H} NMR (CDCl₃) δ (ppm): 156.63 (s, N—CH═N), 139.71 (s,C_(q)), 136.37 (s, C_(q)), 131.18 (s, C_(q)), 116.11 (s, Ar), 114.07 (s,Ar), 97.96 (s, Ar), 68.69 (s, CH₂—O), 34.03 (s), 32.80 (s), 29.50 (m),29.39 (s), 28.72 (s), 28.14 (s), 26.04 (s).

(iii) Synthesis of 5-(12-Azidododecyloxy)-1H-benzo[d]imidazole

5-(12-Bromododecyloxy)-1H-benzo[d]imidazole (381 mg, 1 mmol) was stirredwith sodium azide (78 mg, 1.2 mmol) in DMSO (5 mL) for 4 h. Theresultant mixture was poured into 25 mL of a saturated solution ofNaHCO₃ in water and centrifuged. The desired product was extracted fromprecipitate with CHCl₃ (3×25 mL). Yield 237 mg (69%). ES-MS (m/z) forC₁₉H₂₉N₅O: 343.2387, Calc.: 343.2372. ¹H NMR (DMSO-d₆) δ (ppm): 8.06 (s,1H, N—CH═N), 7.44 (d, 1H, J_(HH)=8.5 Hz, ArH), 7.05 (s, 1H, ArH), 6.78(d, 1H, J_(HH)=7.9 Hz, ArH), 3.95 (t, 2H, J_(HH)=6.5 Hz, —O—CH₂), 3.28(m, 2H, J_(HH)=6.8 Hz, N₃—CH₂), 1.70 (m, 2H), 1.50 (m, 2H), 1.41 (m, br,2H), 1.23 (m, br, 14H). ¹³C{¹H} NMR (CDCl₃) δ (ppm): 154.88 (s, N—CH═N),141.39 (s, C_(q)), 137.78 (s, C_(q)), 133.45 (s, C_(q)), 116.27 (s, Ar),111.75 (s, Ar), 98.19 (s, Ar), 67.89 (s, CH₂—O), 50.61 (s, CH₂—N₃),28.98 (s), 28.89 (s), 28.78 (m), 28.50 (s), 28.21 (s), 26.11 (s), 25.58(s).

(iv) Synthesis of1,3-Diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d]imidazolium iodide

To a suspension of 5-(12-azidododecyloxy)-1H-benzo[d]imidazole (34.4 mg,0.1 mmol) and Cs₂CO₃ (39 mg, 0.11 mmol) in acetonitrile (4 mL),2-iodopropane (250 μL, 2.5 mmol) was slowly added. The mixture wasstirred at 90° C. in a sealed pressure tube under a nitrogen atmospherefor 24 h. The excess of 2-iodopropane, solvent and volatiles wereevaporated in vacuo. The resulting oil was triturated with diethyl ether(2 mL) to give the desired product as a gray powder. Yield 36 mg (65%).ES-MS (m/z) for C₂₅H₄₂N₅O: 428.3397, Calc.: 428.3389. ¹H NMR (CDCl₃) δ(ppm): 10.67 (s, 1H, N—CH═N), 7.65 (d, 1H, J_(HH)=9.2 Hz, ArH), 7.22 (d,1H, J_(HH)=9.3 Hz, ArH), 7.11 (s, 1H, ArH), 5.12 (sept, J_(HH)=6.6 Hz,2H, CH—(CH₃)₃), 4.06 (t, 2H, J_(HH)=6.1 Hz, O—CH₂), 3.24 (t, 2H,J_(HH)=6.6 Hz, N₃—CH₂), 1.84 (m, 12H), 1.59 (m, 2H), 1.49 (m, 2H), 1.28(m, br, 16H). ¹³C{¹H} NMR (CDCl₃) δ (ppm): 158.76 (s, C_(q)), 138.52 (s,N—CH═N), 132.01 (s, C_(q)), 124.70 (s, C_(q)), 117.29 (s, Ar), 114.46(s, Ar), 96.62 (s, Ar), 69.30 (s, CH₂—O), 52.37 (s, CH₃—CH—CH₃), 51.94(s, CH₃—CH—CH₃), 51.41 (S, CH₂—N₃), 29.43 (s), 29.27 (s), 29.04 (s),28.97 (s), 28.74 (s), 26.61 (s), 25.91 (s), 22.26 (s, CH₃), 22.18 (S,CH₃).

(v) Synthesis of1,3-Diisopropyl-5-(12-(azido)dodecyloxy)-1H-benzo[d]imidazole-2-ylidene,(“NHC-6”)

Free carbene was obtained by dissolving1,3-diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d]imidazolium iodide (5.5mg, 0.01 mmol) in 2 mL of anhydrous THF in a round bottomed flask withstirring in a glove box. Separately, a basic solution was prepared ofKO^(t)Bu (1.1 mg, 0.01 mmol) dissolved in 0.7 mL of anhydrous THF. Bothsolutions were cooled to −40° C. The basic solution was then addeddropwise over 30 min. The reaction was stirred for an additional hour.THE was then evaporated in vacuo, and a resulting solid was dissolved intoluene and filtered through Celite® and used directly for surfacefunctionalization.

Example 1D. Four Step Synthesis of5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium HydrogenCarbonate (NHC-1 Hydrogen Carbonate Salt) (i)4-(dodecyloxy)-2-nitroaniline

To a solution of 4-amino-3-nitrophenol (1.540 g, 10 mmol) and1-bromododecane (2.739 g, 2.633 mL, 11 mmol) in anhydrous acetonitrile(50 mL), potassium carbonate (1.380 g, 10 mmol) was added. The mixturewas stirred at 80° C. for 8 h under argon. Then the solvent wasevaporated and crude product was separated by flash-chromatography usinghexane-ethylacetate gradient mixtures. Yield: 2.444 g (76%). Anal. Calc.for C₁₈H₃₀N₂O₃: C, 67.05; H, 9.38; N, 8.69. Found: C, 66.44; H, 9.42; N,8.61. TOF MS (m/z) for C₁₈H₃₀N₂O₃: 322.2247, Calc.: 322.2256 ¹H NMR(CDCl₃): δ 7.35 (d, 1H, J_(HH)=2.8), 7.23 (s, 2H, NH₂), 7.13 (dd, 1H,J_(HH)=9.3, J_(HH)=2.8), 6.97 (d, 1H, J_(HH)=9.3), 3.89 (t, 2H,J_(HH)=6.6, —O—CH₂—), 1.67 (tt, 2H, J_(HH)=6.8), 1.38 (m, 2H), 1.24 (m,16H), 0.85 (t, 3H, J_(HH)=6.8). ¹³C{¹H} NMR (CDCl₃): δ 148.99 (s, C_(g),>CO—CH₂—), 142.29 (s, Co, >C—NH₂), 129.59 (s, C_(q), >C—NO₂), 127.90 (s,C_(Ar)), 121.15 (s, C_(Ar)), 106.28 (s, C_(Ar),), 68.50 (s, —CH₂—O),31.75, 29.4, 29.45, 29.41, 29.17, 29.15, 29.00, 25.89, 22.54, 14.38.

(ii) 5-(dodecyloxy)-1H-benzo[d]imidazole

Formic acid (35 mL) was added to a mixture of4-(dodecyloxy)-2-nitroaniline (2.257 g, 7 mmol), iron powder (3.906 g,70 mmol), and ammonium chloride (3.738 g, 70 mmol) in isopropyl alcohol(49 mL). Resulting mixture was stirred at 80° C. for 3 h, then cooled toroom temperature and filtered off. Solid phase on the filter was washedby isopropyl alcohol (3×5 mL). Filtrate was evaporated to dryness and 30mL of saturated sodium bicarbonate solution was added (foamy). Thensodium bicarbonate (powder) was added portion-wise until pH 6 wasreached. Then the suspension was extracted by chloroform (5×30 mL).Combined non-aqueous layers were dried over anhydrous magnesium sulfate,and evaporated to give 1.715 g of product. Yield 81%. Anal. Calc. forC₁₉H₃₀N₂O: C, 75.45; H, 10.00; N, 9.26. Found: C, 75.09; H, 10.03; N,9.08. TOF MS (m/z) for C₁₉H₃₀N₂O: 302.2348, Calc.: 302.2358. ¹H NMR(CDCl₃): δ 8.00 (s, 1H), 7.55 (d, 1H, J_(HH)=8.6), 7.09 (s, 1H), 6.95(d, 1H, J_(HH)=7.4), 3.89 (t, 2H, J_(HH)=6.5, —O—CH₂—), 1.81 (tt, 2H,J_(HH)=7.3), 1.46 (m, 2H), 1.35 (m, 2H), 1.27 (m, 14H), 0.89 (t, 3H,J_(HH)=6.9). ¹³C{1H} NMR (CDCl₃): δ 155.84 (s, C_(q), >CO—CH₂—), 140.34(s, C_(Ar), N═CH—NH), 133.64 (s, C_(q)), 130.76 (s, CO_(q)), 116.32 (s,C_(Ar)), 112.64 (s, C_(Ar)), 97.86 (s, C_(Ar)), 68.52 (s, 1C, —CH₂—O—),31.74, 29.44, 29.27, 29.17, 25.96, 22.49, 13.88.

(iii) 5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide

To a suspension of 5-(dodecyloxy)-1H-benzo[d]imidazole (302.4 mg, 1mmol) and Cs₂CO₃ (325.8 mg, 1 mmol) in acetonitrile (50 ml),2-iodopropane (4.25 g, 2.5 mL, 25 mmol) was slowly added. The mixturewas stirring at 90° C. in a flask with reflux condenser under nitrogenatmosphere for 24 h. Then the excess of 2-iodopropane, solvent andvolatile sub-products were evaporated under vacuum. The residual solidwas triturated and sonicated in diethyl ether (2×4 mL), which was thendecanted off. Subsequent drying under vacuum afforded the desiredproduct as an off-white powder (342 mg, 66% yield). Anal. Calc. forC₂₅H₄₃N₂OI: C, 58.36; H, 8.42; N, 5.44. Found: C, 56.80; H, 8.39; N,5.52. TOF MS (m/z) for C₂₅H₄₃N₂O: 387.3389, Calc.: 387.3375. ¹H NMR(CDCl₃): δ 10.59 (s, 1H, N—CH═N), 7.67 (d, 1H, J_(HH)=9.0), 7.21 (d, 1H,J_(HH)=9.0), 7.13 (s, 1H), 5.15 (sept, J_(HH)=6.8, 2H, CH—(CH₃)₂), 4.06(t, 2H, J_(HH)=6.3, —O—CH₂—), 1.84 (tt, 12H, J_(HH)=6.5, CH—(CH₃)₂),1.82 (m, br, 2H), 1.48 (m, 2H), 1.25 (m, 16H), 0.86 (t, 3H, J_(HH)=6.6).¹³C{¹H} NMR (CDCl₃): δ 158.88 (s, CO_(q), >CO—CH₂—), 138.45 (S, C_(Ar),N═CH—NH), 132.10 (s, CO_(q)), 124.79 (S, CO_(q)), 117.41 (S, C_(Ar)),114.58 (S, C_(Ar)), 96.79 (s, C_(Ar)), 69.45 (s, 1C, —CH₂—O—), 52.42 (s,CH—(CH₃)₂), 52.0 (S, CH—(CH₃)₂), 31.88, 29.62, 29.59, 29.55, 29.51,29.34, 29.30, 29.03, 25.98, 22.64, 22.35 (s, CH—(CH₃)₂), 22.27 (s,CH—(CH₃)₂), 14.06 (s. CH₃).

(iv) 5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium HydrogenCarbonate

A mixture of 5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-iumiodide (257.1 mg, 0.5 mmol) and dry KHCO3 (55.0 mg, 0.55 mmol) inanhydrous MeOH (12 mL) was stirred at room temperature for 48 h. Theresulting yellow solution was filtered, and its filtrate was evaporatedto dryness under vacuum. The residue was extracted with dichloromethane(6 mL), and the solution was filtered through a Celite® pad. Evaporationto dryness of the filtrate gave the product as a yellowish solid (203mg, 90%). Time-of-flight mass spectrometry (“TOF MS”) (m/z) forC₂₅H₄₃N₂O: 387.3389, Calc.: 387.3375. ¹H NMR (CDCl₃): δ 10.74 (s, 1H,N—CH═N), 7.65 (d, 1H, J_(HH)=9.0), 7.22 (d, 1H, J_(HH)=9.0), 7.10 (s,1H), 5.15 (sept, J_(HH)=6.8, 2H, CH—(CH₃)₂), 4.06 (t, 2H, J_(HH)=6.3,—O—CH₂—), 1.84 (m, 12H, CH—(CH₃)₂), 1.81 (m, br, 2H), 1.49 (tt, 2H,J_(HH)=7.4), 1.37 (tt, 2H, J_(HH)=7.5), 1.26 (m, 14H), 0.88 (t, 3H,J_(HH)=6.6). ¹³C{¹H} NMR (CDCl₃): δ 158.79 (s, C_(q), >CO—CH₂—), 138.71(s, C_(Ar), N═CH—NH), 132.04 (s, C_(q)), 124.74 (s, C_(q)), 117.28 (s,C_(Ar)), 114.47 (s, C_(Ar)), 96.69 (s, C_(Ar)), 69.34 (s, 1C, —CH₂—O—),52.43 (s, CH—(CH₃)₂), 52.0 (s, CH—(CH₃)₂), 31.85, 29.60, 29.58, 29.53,29.31, 29.29, 28.99, 25.95, 22.62, 22.28 (s, CH—(CH₃)₂), 22.20 (s,CH—(CH₃)₂), 14.05 (s. CH₃).

Example 1E. General Experimental Protocol for Benizimidazole CarbonateSynthesis

Preparation of [iPr₂BIMY(H)][HCO₃] (“Carbonate Salt of NHC-1”):

A similar procedure to Taton, Fèvre, M., et al. J. Am. Chem. Soc. 2012,134 (15), 6776-6784 and Fèvre, M., et al. J. Org. Chem. 2012, 77 (22),10135-10144 was followed. 1,3-Diisopropyl-1H-benzo[d]imidazol-3-iumiodide (258 mg, 0.781 mmol) and KHCO₃ (86.1 mg, 0.859 mmol) were driedfor several hours under vacuum at room temperature. 5 mL of dry methanolwas added under argon and this was stirred for 48 hours at roomtemperature. The methanol was removed in vacuo and 5 mL ofdichloromethane was added. This suspension was filtered through Celite®,the resulting filtrate was evaporated under vacuum. A resulting powderwas washed with hexanes to yield an off-white powder (99+% yield). Theabove procedure was used to prepare carbonate salts of other NHCs.

As will be recognized by a person of ordinary skill in the art of theinvention, ¹H NMR and ¹³C NMR characterization data for a carbonate saltof an NHC is substantially identical to the characterization data of thecorresponding NHC's iodo salt from which it was prepared. For thisreason, mass spectroscopy was used to show that the carbonate salt wasobtained. Representative characterization data is provided below for thecarbonate salt of NHC-1.

Carbonate salt of NHC-1 also known as [Pr₂BIMY(H)][HCO₃]: ¹H NMR (600MHz, Methanol-d₄) δ 1.74 (d, 12H, (CH₃)₂, J=6.7 Hz), 5.10 (m, CH(CH₃)₂),7.71 (dd, J=3.1 Hz, 6.3 Hz, 2H, Hbenz), 8.04 (m, J=2.5 Hz, 5.7 Hz, 2H,Hbenz), 9.63 (br, 1H, N₂CH). HCO₃-proton could not be observed due torapid exchange with the deuterated solvent on the NMR time scale, N₂CHcould be detected as broad signal from the same reasons. ¹³C NMR (150.8MHz, Methanol-d₄) δ 21.1, 51.4, 113.6, 126.2, 132.9. High ResolutionMass Spectrometry: Positive mode: calc for [C₁₃H₁₉N₂]⁺ [M]⁺ 203.1543,found 203.1532; negative mode: calc for [HCO₃]⁻ 60.9931; found 60.9939.

Example 1F. Synthesis of 1,3-Dimethylbenzimidazolium Hydrogen Carbonate,[Me₂BIMY(H)][HCO₃], NHC-17

1,3-dimethylbenzimidazolium iodide [Rodriguez-Castillo, M. et al.,Dalton Trans. 2014, 43, 5978-5982] (200 mg, 0.730 mmol) and KHCO₃ (76.71mg, 0.766 mmol) were dried for several hours under vacuum at roomtemperature. Dry methanol (5 mL) was added under argon and a resultantmixture was stirred for 48 hours at room temperature. The mixture'svolume was removed in vacuo and dichloromethane (5 mL) was added to forma suspension. This suspension was filtered through CELITE® and afiltrate was collected. The filtrate's volume was reduced under vacuumand a resulting powder was obtained. The powder was washed with hexanesand an off-white powder was collected by filtration (NHC-17, 112.5 mg,74%). ¹H NMR (400 MHz, methanol-d₄) δ 9.48 (br, 1H, N₂CH), 7.97 (dd,J=6.3, 3.1 Hz, 1H, CH_(A)r), 7.73 (dd, J=6.3, 3.1 Hz, 1H, CH_(A)r), 4.17(s, 3H, CH₃). ¹³C NMR (100 MHz, methanol-d₄) δ 133.47 (C_(q)), 128.11(CH_(A)r), 114.23 (CH_(A)r), 34.03 (CH₃). The HCO₃ ⁻'s proton and carboncould not be observed due to rapid exchange with the deuterated solvent.HRMS (ESI): Positive mode: calcd. for [C₁₁H₁₅N₂]⁺ 147.0917, found147.0910; negative mode: calcd. for [CO₃]⁻ 59.9847, found 59.9861. XPS:N:C ratio found 2:10; N:C ratio expected 2:9.

Example 2. Deposition of Carbenes on Gold Surfaces

Self-assembled monolayers were prepared by immersion of gold substratesin a 1 mM solution of a NHC-carbene in anhydrous toluene, for 4 h atroom temperature in a glove box. Substrates then were rinsed inanhydrous THF (5×2 mL) and dried under a nitrogen gas stream.

To test NHCs' ability to form stable monolayers, Au(111) films on micaand thioether-protected gold nanoparticles were treated withrepresentative NHCs: NHC-1, NHC-2, NHC-3, NHC-4, NHC-5A, NHC-5B, NHC-6,NHC-7, NHC-8, NHC-9, NHC-10, NHC-11, NHC-13, NHC-14, NHC-15, NHC-16,NHC-17, and NHC-18 (see Table 1 for structural formulae).

Each carbene was found to react with Au surfaces after simple roomtemperature immersion of Au(111) or Au nanoparticles in a solution ofthe carbene or the corresponding carbonate salt in an appropriatesolvent. Despite considerable variety in structure, C/N ratios, asdetermined by X-ray photoelectron spectroscopy (XPS), were in agreementwith the representative NHCs within error, indicating clean reactionwith the surface (see Table 2A and 2B). Scanning tunneling microscopy(STM) was also used to analyze selected films (FIGS. 2B and 5).

XPS data showed complete removal of dodecylsulfide from the surface ofgold nanoparticle surfaces upon treatment with a 1 mM solution of a NHCin toluene at room temperature for as little as 4 h (see FIGS. 1A and1B). XPS spectra obtained after reacting NHC 1 (IPrBenz) with goldnanoparticles protected with dodecylsulfide showed that no S(2p) XPSsignal was observed, indicating complete displacement of dodecylsulfideby NHC-1 within an XPS' limits of detection (FIG. 1C). Similarly, onceNHC-protected Au nanoparticles were formed, treatment with dodecylsulfide resulted in no incorporation of sulfur within the limits ofdetection. Thiols such as dodecanethiol were also incapable of removingrepresentative carbenes from NHC-terminated Au(111). After treatingNHC-1-protected Au(111) surfaces with a 1 mM solution of dodecanethiolfor 24 h at room temperature, no sulfur was detected by XPS (FIG. 2E).

Although dodecyl sulfide was completely removed upon treatment withNHCs, gold surfaces initially functionalized with dodecanethiol weremore resistant to displacement by NHC. Only a 60% loss in the S(2p)signal was observed following 24 h exposure of dodecanethiol protectedAu(111) surfaces to a solution of NHC-1 or NHC-3 (FIGS. 3D and 3E).Concomitant with the decreased S(2p) signal, an N(1s) signal appeared,which indicated that NHCs were deposited on the Au surface, but completethiol-displacement was not achieved under the same conditions as thedialkylsulfides. Without wishing to be bound by theory, lowered stericbulk of the thiol vs. sulfide and the specific bonding mode of the thiolcompared to the carbene, as described below, were considered potentiallyresponsible for this phenomenon.

Example 3. Studies of pH Stability Tests

Since stability in thiol-based SAMs was closely related to ordering [C.Vericat, M. E. Vela, G. Benitez, P. Carro, R. C. Salvarezza, Chem. Soc.Rev. 39, 1805 (2010)], and NHC-1-based films displayed molecular levelordering, the stability of these films was explored. SAMs formed fromNHC-1 showed no change by XPS after heating in boiling solvent (e.g.,THF) for 24 hours. For stability test results see FIG. 2C and Table 3.SAMs of NHC-1 also showed no discernible change upon heating in boilingwater for 24 hours in air, demonstrating thermal and oxidativestability. A large fraction of the surface even remained upon treatmentwith 1% H₂O₂ for 24 h. Although decomposition was observed at 3% H₂O₂(see FIG. 8), the fact that 80±5% of the film survived treatment with 1%H₂O₂ for 24 h was notable and would not be possible with thiol-basedSAMs. Films of NHC-1 were also completely stable in aqueous solutionsranging from pH 2 to 12 for 24 h (see FIG. 9 and Table 3 of FIG. 23).

When the bulkier carbene 3 was employed to generate a SAM, completestability to boiling THE (66° C.) was still observed (FIG. 2D), howevergreater than 50% loss of the film was observed in boiling water (FIG.2D). These observations were consistent with the higher ordering ofNHC-1-based films seen in the STM images. Similar to regular alkylthiol-based SAMs, where stability was provided by both gold thiolatebonds and van der Waals interactions between the alkyl groups [R. G.Nuzzo, et al. J. Am. Chem. Soc. 105, 4481 (1983); B. D. Gates, et al.Chem. Rev. 105, 1171 (2005); J. C. Love, et al. Chem. Rev., 105, 1103(2005); U. Drechsler, et al. Chem.—Eur. J. 10, 5570 (2004); C. D. Bain,et al. J. Am. Chem. Soc. 111, 321 (1989)], the ability to stack providedenhanced stability for benzimidazole-based SAMs based on NHC-1. Inaddition, the smaller isopropyl wing-tip substituents of NHC-1 comparedto the mesityl substituents on NHC-3 likely provided for greater packingdensity on the surface.

NHC-1-functionalized gold surfaces were submerged in freshly preparedunbuffered solutions of certain pHs for 24 h. Experiments were conductedunder N₂ gas to minimize the possibility of pH change due to adsorptionof atmospheric CO₂. After this time, functionalized surfaces were rinsedin deionized water (3×2 mL) and dried in an N₂ gas stream. pH valueswere adjusted using NaOH and HCl solutions. Unbuffered solutions wereemployed in order to avoid potential adsorption effects of buffer ionsfrom solution. Ionic strength of all solutions was maintained at 10⁻³ Mfor all solutions, except those under the extreme pH 2 and 12 regimes.See Table 3 of FIG. 23 for a summary of the results of these stabilitytests.

Example 4. Deposition of Carbenes from Carbene Precursors on GoldSurfaces Example 4A. Initial Studies

Bis(mesityl)immidazolium salt (IMesHCO₃) was prepared in 52% yield byfollowing a reported literature procedure [Taton, D., et al. J. Am.Chem. Soc. 2012, 134, 6776.] Three different IMesHCO₃-gold depositionmethods were investigated: (1) IMesHCO₃ (4 mg) was dissolved in wetmethanol under air and a gold slide was completely submerged into themethanolic solution. Reaction was left under Argon for 48 h at roomtemperature. The gold slide was then washed with 4 mL of methanol, driedunder air and XPS data were recorded; (2) IMesHCO₃ (2 mg) was dissolvedin dry methanol under air atmosphere and a gold slide was completelysubmerged into the methanolic solution. Reaction was left under argonfor 48 h at room temperature. The gold slide was then washed 15 times×4mL of methanol dried under air and XPS data were recorded; (3) IMesHCO₃(2 mg) was dissolved in dry methanol under argon (using a Schlenk line)and a gold slide was completely submerged into the methanolic solution.Reaction was left under argon for 48 h at room temperature. The goldslide was then washed 15 times×4 mL of methanol dried under air and XPSdata were recorded. XPS spectra clearly showed deposition of NHC-3carbene on all three gold surfaces and no difference in signal intensitywas observed for all experiments (see FIG. 15).

Example 4B. Studies of Carbene Precursors Including Carbonate Salts ofVarious NHCs

Studies have been conducted of carbene precursor compounds such as, forexample, carbonate salt of benzimidazole and several of its derivatives.Carbonate salts of NHCs offer an improved means of forming carbeneself-assembled monolayers on a metal surface, since carbonate salts andsolutions of carbonate salts are air stable. Furthermore, carbonatesalts of NHCs enable deposition that can take place in solvents thathave not undergone any special treatment to exclude water or oxygen.Therefore, a carbene monolayer precursor (e.g., carbonate salts of NHCs)can be stored under ambient conditions, and no special conditions (suchas exclusion of water or oxygen) are required to prepare a carbeneself-assembled monolayer. This is an improvement over simple carbenes,which must be stored under an oxygen-reduced atmosphere (e.g., in aglovebox) and reacted with a dry surface under anaerobic conditions.

Resulting carbene self-assembled monolayers on Au prepared usingcarbonate salts of NHCs exhibited identical XPS spectra and stabilitytowards extremes of pH, solvent and oxidizing agents (H₂O₂) asself-assembled monolayers prepared from NHCs.

Self-assembled monolayers were prepared by immersion of the goldsubstrates in solutions of the corresponding hydrogen carbonateprecursor (up to 2 mM) in methanol for up to 24 h at room temperature.Substrates then were rinsed in methanol (5×2 mL) and dried under anitrogen gas stream.

Example 5. Nanoparticles Studies Example 5A. Preparation of GoldNanoparticles

Chloroauric acid tetrahydrate 52 mg, 0.126 mmol of in water (5.1 mL) wasadded to a solution of tetraoctylammonium bromide (167 mg, 0.306 mmol)in toluene (3.06 mL). The resulting mixture was stirred vigorously untilthe aqueous layer became colourless. Following this, a solution ofdodecyl sulfide (170 mg, 0.459 mmol) in toluene (11.5 mL) was added andallowed to stir for another 5 minutes. A solution of sodium borohydride(69.5 mg, 1.837 mmol) in water (18 mL) was added in one aliquot to themixture while stirring. A fast colour change from red-orange to darkpurple-brown was observed, indicating colloid formation. The solutionwas allowed to stir for another hour before a non-aqueous layer wasseparated and reduced to a minimum amount through rotary evaporation atroom temperature (to prevent nanoparticle decomposition). The colloidswere then suspended in anhydrous ethanol and left at room temperatureovernight to precipitate. The resulting solution was then centrifuged(2500 rpm, 1 hour), decanted and dried in vacuo. The nanoparticles werethen suspended in ethanol (3×10 mL), centrifuged, dried and stored at−40° C. in solid form.

Example 5B. Studies of Dodecyl Sulfide Exchange by NHCs in GoldNanoparticle

Gold nanoparticles stabilized by dodecyl sulfide (3 mg) were dissolvedin anhydrous toluene (5 mL) under an inert atmosphere in a glove box andthen a 20-fold molar excess of carbene relative to gold was added. Thismixture was allowed to react overnight at room temperature.Nanoparticles (except NHC-1 stabilized) were collected bycentrifugation, washed with toluene (3×0.5 mL) and dried in vacuo. NHC-1stabilized nanoparticles in toluene were mixed with hexane (2 mL)collected by centrifugation, washed with hexane (3×0.5 mL), centrifuged,and dried in vacuo.

Example 5C. Studies of NHCs in Palladium Nanoparticles IncludingFunctionalization of Dodecylsulfide Stabilized Pd Nanoparticles withNHCs

Palladium nanoparticles were prepared from PdCl₂ by a methoddemonstrated by Brust et al. [Brust, M., et al., Journal of the ChemicalSociety—Chemical Communications 1994, 801]. Dodecyl sulfide was used asa stabilizer in a two-phase preparation. PdCl₂ (0.24 mM) was mixed with10 ml diluted HCl (0.5M) to form a Pd solution. Separately,tetraoctylammonium bromide (TOABr) (0.30 g), a phase transfer catalyst,was added to 20 mL of toluene. This TOABr mixture was added to the Pdsolution and the resulting reaction mixture was stirred vigorously for20 min. 0.5 mM of dodecyl sulfide was added to the reaction mixture andit was stirred for a further 20 minutes. An aqueous solution of NaBH₄ (1mM, in 5 mL water) was added to the reaction mixture to reduce Pd(II)ions to Pd(0). Within a few seconds, the reaction mixture solutionturned dark black confirming formation of Pd(0). Stirring was continuedfor 2 hrs to allow docecylsulfide stabilized Pd nanoparticles (“Pd-NP”)to form. Size of the nanoparticles was controlled by varying theconcentration of stabilizing agents. Table 4 lists concentration ofstabilizing agents and size of resulting Pd nanoparticles.

Resulting dodecyl sulfide-stabilized Pd nanoparticles were treated witha NHC-1 solution. Dodecylsulfide-stabilized Pd nanoparticles (6 mg) weredispersed in 2 mL toluene by sonication for 5 minutes. A 10 mM solutionof NHC-1 was prepared in 2 mL isopropanol. 2 mL of the Pd nanoparticledispersion and 2 mL of the NHC-1 solution were then mixed together. Thereaction mixture was maintained at room temperature for 24 hours withvigorous stirring. Following this time period, the nanoparticles wereseparated by centrifugation. Then the nanoparticles were washed intoluene using a sonicator and then separated by centrifugation. Thiswashing and separating was repeated three times to remove loosely boundor mobile reagents.

FIG. 20 shows XPS data for NHC-terminated Pd nanoparticles. Spectra wereidentical from all nanoparticle size distributions. Residual S wasobserved for the NHC-1-Pd nanoparticles, as evidenced by the presence ofthe S 2p peak in the XPS spectra. A strong N 1s signal was alsoobserved, which is consistent with binding of NHC-1 to the Pdnanoparticle surface. The relative atomic ratios of N:S and C:N asdetermined by XPS are indicated in Table 4. The C:N ratio in the twosmaller nanoparticles is only slightly larger than the expectedstoichiometric value of 6.5 (wherein only NHC would be on the surface).Unlike the Au nanoparticles, the S signal was not completely missing forthe Pd nanoparticles. However, it was considered likely that dodecylsulfide was no longer present in large quantities, otherwise a muchhigher C:N ratio would have been observed. The relatively small N:Sratio of the experimental results indicated that some S remains. Withoutwishing to be bound by theory, the inventors suggest that there may besome PdS within the outer shell of the nanoparticle.

Example 6. Computational Studies

Density functional theory (DFT) calculations were performed to examinestructural features and binding energies of NHC-1 on gold slabspresenting the (111) surface (FIG. 4). To construct slabs, theface-centered cubic (fcc) unit cell of gold was optimized according amethod described below. Resulting lattice constant was 4.107 Å, which isin good agreement with literature values of 4.080 Å [C. KittelIntroduction to Solid State Physics, 7^(th)ed. (John Wiley & Sons, NewYork, 1996)]. An Au (111) surface was cleaved from a bulk structure anda resulting hexagonal cell was repeated twice in lateral directions. Theslabs used in these calculations were four layers thick. These testsshowed this thickness was sufficient to converge surface energies tobetter than 1 mJ/m². The monomer was then added to the upper surface ofthe slab at positions corresponding to a-top, bridging, and three-foldsites. These structures were relaxed while keeping the positions of thegold atoms in the bottom two layers of the slab fixed at their bulkpositions. Analogous calculations were performed on the bare slab, i.e.atoms in the upper two layers were relaxed while keeping those in thebottom two layers at fixed positions, and on the monomer, where allatoms were allowed to relax. The heights of the cells used in thecalculations with the slab models were selected to ensure that at least10 Å of vacuum space was present between periodic images. In addition,dipole correction techniques [Bengtsson, L. Physical Review B 59, 12301(1999)] were employed to eliminate spurious electrostatic interactionsbetween periodic images along a direction normal to the slabs.

All DFT calculations were performed using the PBEsol exchangecorrelation functional [Perdew, J. P., et al. Phys. Rev. Lett. 100,136406 (2008)]. Core electrons were treated with projector augmentedwavefunction potentials [Blöchl, P. E. Physical Review B, 50, 17953(1994)] including scalar relativistic effects on all atoms. The valencestates were represented with a planewave basis set expanded up to akinetic energy cutoff of 40 Ry (Rydberg constant), and a kinetic energycutoff of 400 Ry was used to represent the augmentation charges. Thislevel of theory reproduces experimental Au—C bond lengths of selectedcompounds [Xu, X., et al. Organometallics 32, 164 (2013)] to within0.012 Å. A 3×3×1 set of k-points was used in the calculations involvingslabs. These details were sufficient to converge the total energies ofthe systems examined to better than 1 meV/atom. All calculations wereperformed with the Quantum-Espresso simulation package [Giannozzi, P.,et al. J. Phys.: Condensed Matter 21, 395502 (2009)].

Example 6A: DFT Studies on C—Au Bond Strength

Bonding of NHC-1 at an Au(111) surface was simulated by DFT methods andwas characterized by a very different bonding mode as compared to thiolSAMs. Details of the strength and nature of the interactions of NHC 1with an Au(111) film on mica appear in FIG. 4. With respect tothiol-modified gold surfaces, thiols were typically expected to bind togold via three-fold hollow (tetrahedral) sites [H. Häkkinen, NatureChem. 4, 443 (2012)], with a reported binding energy of 127 kJ/mol [D.J. Lavrich, et al. J. Phys. Chem. B 102, 3456 (1998)]. However, withrespect to the current DFT studies, the calculations indicated that thisgeometry lead to the least stable configuration for the NHC-goldsurface, with an Au—C bond strength of 70.3 kJ/mol (FIG. 4, right).NHC-1 preferred to bind to a-top sites via a single gold-carbon bond(FIG. 4, centre), with a calculated bond strength of 149 kJ/mol, 22kJ/mol greater than that of thiols on Au(111) [H. Häkkinen Nature Chem.4, 443 (2012)]. The Au—C bond length was calculated to be 2.118 Å, whichwas fully consistent with that observed in molecular gold-NHC species[X. Xu, et al. Organometallics 32, 164 (2013)].

DFT results were consistent with the observation that an NHC-protectedAu(111) surface was impervious to adsorption of thiols, but that athiol-terminated surface could not be completely exchanged for NHC.Without wishing to be bound by theory, it has been suggested that bothspecies compete for different binding sites on the surface, and thesmaller thiol, sitting in the lower threefold hollow site, was morereadily retained, while the larger NHC sits above it on the a-top site.The fact that a preformed NHC—Au surface was not affected by treatmentwith thiols under the conditions described as determined by XPS analysisimplies that: (i) a gold-carbene bond was at least as strong as agold-thiol bond; and (ii) once formed, NHC surface coverage was denseenough to prevent even dodecanethiol from penetrating and binding tosites not covered by the NHC.

Example 7. STM Characterization of Monolayer Formation

STM images of NHC-1 deposited on Au(111) films were characterized bydensely packed SAMs with molecular-level resolution (FIG. 2A). Localordering was apparent throughout the entire film. STM images of NHC-1deposited on Au(111) from the carbonate salt were characterized bydensely packed SAMS with molecular-level resolution exhibitinglong-range ordering over many thousands of unit cells (FIG. 2B).Individual features were approximately 4.8 Å×3.4 Å, and were generallyaligned along the shorter axis (FIG. 2A). This was consistent with thebenzimidazole portion of the carbene sitting upright on the surface, andforming n-stacks with neighbouring molecules.

The STM images showed the presence of darker regions, one Au layer indepth, which were not present on the unreacted Au(111) film. Theseregions were areas in which restructuring of the Au surface had takenplace, were analogous to the “etch pits” commonly seen on Au(111)surfaces treated with alkanethiols [C. Vericat, et al., Chem. Soc. Rev.39, 1805 (2010)]. These were not defects in the SAM itself, and stackedNHCs could also be observed within the dark features (see FIG. 2A). TheSTM image of NHC-1 on Au(111) (FIGS. 2A and 2B) showed no evidence ofislands. However, islands were clearly present in the STM image of NHC-3on Au(111) (see FIG. 5). The density of darker regions was larger forNHC-3 compared with films prepared from NHC-1 (see FIGS. 6 and 7). Thisobservation was consistent with NHC-3 forming a less well-ordered SAM,as the presence of a high density of step edges associated withislanding may be necessary to accommodate the bulky mesityl side groupsof the NHC. Films of NHC-3 on Au(111) were characterized by IMes units(small bright spots) that were not self-assembled into orderedstructures (FIG. 5). As the mesityl side groups of NHC 3 wereconsiderably bulkier than the isopropyl groups of NHC-1, a lessorganized and more loosely packed SAM was expected at the Au(111)surface.

Example 8: Surface Functionalization

Aromatic substitution and S_(N) ²-chemistry permitted preparation ofcarbene NHC-6, an analog of NHC-1 in which an alkyl chain terminatedwith an azide functional group was attached to the benzimidazole unit(FIG. 3A). SAMs on Au(111) derived from NHC-6 were prepared, and theresulting azide-terminated surfaces were interrogated by XPS and contactangle measurements (FIG. 3). When films of NHC-6 on Au(111) were exposedto aqueous Cu solutions in the presence of the hydrophilic alkynepropargyl alcohol, the expected Huisgen cycloaddition (click reaction)took place resulting in the formation of triazole species on the SAM(FIG. 3A). The success of this reaction was monitored by XPS and contactangle measurements (FIGS. 3B and 3C). The latter technique confirmedthat the azide-terminated surface with a contact angle of 78±3° wastransformed to an alcohol-terminated surface with the expected contactangle of 45±3°. Treatment of the same surface in the absence of eitherCu or the alkyne resulted in no discernible change in the contact angle.

XPS analysis of Au(111) surfaces modified by NHC-6 displayed threedistinct signals in the N(1s) region of the spectrum, which wereassigned to the two virtually identical nitrogen atoms comprising theN-heterocyclic carbene ring, the two terminal nitrogen atoms of theazide, and the very diagnostic central nitrogen of the azide (FIG. 3B).This latter atom appeared at significantly higher energy than the otherssince it is flanked by two other electronegative nitrogen atoms.Consistent with a successful Huisgen cycloaddition having occurred onthe surface, this signal was lost after exposure of the surface topropargyl alcohol and Cu catalyst (FIG. 3C). After this reaction, theN(1s) region of the XPS spectrum was characterized by only two distincttypes of N atoms, which was consistent with the transformation of theazide to a triazole, and the contact angle change was consistent withthat of an alcohol-terminated surface.

Example 9. SPR Experiments with NHC-16 and Comparison to Commercial“HPA” Chip

A Surface Plasmon Resonance (SPR) chip was prepared by depositing aNHC-16 self-assembled monolayer on a blank Au chip (blank Au availablefrom Biacore, General Electric, Pittsburgh, Pa., USA). The resultingchip was consequently coated with a hydrophobic layer, which can be usedto form a model lipid layer on its surface. Such a lipid layer can beused for detection of biomolecules via SPR. Efficacy of said NHC-16coated chip to form a lipid layer via lecithin adsorption was comparedto the efficacy of a commercially available HydroPhobic Association(HPA) chip (available from Biacore), whose surface was coated with along-chain octadecane-thiol, self-assembled monolayer on a gold surfacein a flat, quasi-crystalline hydrophobic layer.

Example 9A. Stability Tests

The NHC-16 carbene-coated chip operated in a similar fashion to the HPAchip under a wide range of pH conditions. However, there were twoimportant differences. The carbene-coated chip was stable. The chip wasexposed to phosphate buffered saline (PBS) buffer, a solvent to which aSPR chip would be routinely exposed to in a typical experiment, at orabove ambient temperatures. After exposure to PBS buffer at 65° C. for24 hours, the carbene-coated chip's performance was unaffected. Incontrast, the HPA chip was destroyed under these conditions.

Example 9B. Performance

The carbene-coated chip showed better performance since it allowedformation of a single layer of lecithin immediately upon exposure. Incontrast, the HPA chip first adsorbed multilayered lecithin vesiclesthat had to be washed off the HPA chip's surface before it could be usedfurther. The lecithin layer on the carbene-coated chip was highlyreproducible from run to run. The lecithin layer on the carbene-coatedchip was highly resistant to adsorption of BSA protein. BSA is a proteinthat is well known to undergo non-specific binding to bare Au: that isit undergoes indiscriminate physical adsorption to a hydrophobic surfacedue to strong attractive van der Waals' forces. This indicates that theNHC-16 coated chip's overlayer was complete since a non-specific bindingprotein such as BSA would be expected to adsorb on an incompleteoverlayer in which bare hydrophobic sites remain. Performance of thecarbene-coated chip equalled or exceeded the commercial HPA chip in thisregard. See Tables 5A and 5B for comparison data between the HPA chipand the NHC chip. Notably, the carbene-coated chip was more robust andperformed better than a commercially available HPA chip.

Example 9C. Preparation of Lipid Vesicles

Small unilamellar vesicles (SUV) were prepared in phosphate buffer (100mM Na₂HPO₄/NaH₂PO₄, 150 mM NaCl, pH 7.4). The general protocol was asfollows: Egg yolk L-α-phosphatidylcholine (9.0 mg, 2 mM) was dissolvedinto chloroform/methanol (2/1, v/v) in a vial. The solvent mixture wasevaporated under a stream of nitrogen for at least 30 min, yielding athin lipid film on the bottom of the vial. Lipid films were thenthoroughly dried under vacuum for 2 h to remove the solvent mixture.Dried lipid films were hydrated by adding 6.0 mL of running buffer, andthe mixture was then vortexed thoroughly until all lipid films wereremoved from the vial walls. A milky uniform suspension was obtained.Lipid suspensions were frozen in a dry ice/acetone bath for 8 min,followed by thawing in a water bath (80° C., 8 min). This freeze-thawcycle was repeated 8 times. Resultant mixtures were then sonicated untilsuspensions changed from milky to nearly transparent, yielding a uniformsuspension of small unilamellar vesicles with diameters of about 30 toabout 35 nm.

Example 9D. Formation and Regeneration of Lipid Monolayers

Following equilibration of a chip sensor chip to room temperature, thechip was docked and primed with running buffer. All solutions forinjection were freshly prepared, filtered through a 0.2 μm pore filter,and thoroughly degassed prior to use. Sensor surface was preconditionedby a 5-min injection of 40 mM n-Octyl β-D-glucopyranoside (OG) at a flowrate of 10 μL/min. SUV were injected immediately for a period of 25 min,followed by a 5-min dissociation with buffer. To remove any looselybound vesicles, the flow rate was increased to 100 μL/min for a 1 minbuffer rinse followed by a 5-min wash with 50 mM sodium hydroxide at 10μL/min. A stable baseline was obtained, presumably corresponding to alipid monolayer. Degree of surface coverage by lipids was evaluated byinjecting 0.1 mg/mL BSA at a flow rate of 10 μL/min for 5 minutes toassess the quantity of non-specific binding [M. A. Cooper et al.Biochimica et Biophysica Acta 1373, 101-111 (1998)]. After each bindingcycle, the sensor surface was regenerated by injecting 40 mM OG for 5min. Stability of the sensor chips were assayed by repeated cycles ofbinding with egg PC SUV and regenerating with OG. The results shown inTables 5A and 5B demonstrate that, under a wide range of pH conditions,that the carbene chip outperforms the commercial HPA chip in severalways: first, the magnitude of the reduction in phosphatidylcholineloading after the NaOH wash is significantly lower in the carbene chip,indicating that the phosphatidylcholine initially forms a monolayer onthe carbene chip, while on the HPA chip it forms a series of vesiclesthat are removed during the NaOH wash and impede the quality of theoverlayer. Secondly, the reproducibility of the loading in virtually allcases is superior in the carbene chip, as evidenced by the lowerstandard deviation (%) between runs. Thirdly, the extent of BSA bound tothe surface is lower on the carbene chip, indicating a completemonolayer of phosphatidylcholine has been formed on the surface, incontrast to the HPA chip which shows a greater extent of BSA bonding,indicating bare hydrophobic sites remain.

Example 10. Carbenes as a Support for Water Oxidation Catalysis

Using carbonate carbene precursors, an azide-terminated carbenemonolayer self-assembled on gold. Subsequently, a “click” reaction wasperformed on the azide to attach a chosen ligand system. Then anIr-based water oxidation catalyst co-ordinated on the surface. Onceformed, this catalyst's activity to water oxidation was demonstrated byCerium Ammonium Nitrate method (“CAN”), which uses a sacrificial oxidantfor water oxidation.

The transformations shown in Scheme 1 of FIG. 22 have been carried out(up to NHC-10). Intermediate compounds 1 to 6 and NHC-7 and NHC-8 havebeen characterized by XPS and/or NMR spectroscopy. NHC-10 has been usedin preliminary experiments with CAN using UV-vis absorbancespectroscopy. These experiments show that NHC-10 is indeed activetowards CAN destruction, and, with bubbles observed during thisreaction, presumably water oxidation, and can undergo some degree ofrecycling.

Compound 2 was made by placing 1.541 g of compound 1 (10 mmol) and 1 eqof K₂CO₃ (1.382 g, 10 mmol) in a dry round bottom flask under Ar(g). 30mL of dry acetonitrile was added to the flask and the mixture wasstirred until all of compound 1 had dissolved. 3 equivalents of1,6-dibromohexane (4.6 mL, 30 mmol, available from Sigma-Aldrich) wereadded. The resultant mixture was raised to 80° C. and was stirredovernight. The mixture was cooled to room temperature and concentratedunder reduced pressure using a Rotary Evaporator (Buchi). The resultingresidue was passed through a silica flash column using hexanes as thefirst eluent. After 100 mL of solvent the eluent was changed to 7:3hexanes to ethyl acetate. The volume was reduced under reduced pressureusing a Rotary Evaporator. A bright red solid was obtained (compound 2,76% yield).

¹H NMR (CDCl₃) δ: 1.52 (m, 4H), 1.81 (q, J=7.0 Hz, 2H), 1.92 (q, J=7.0Hz, 2H), 3.44 (t, J=6.5 Hz, 2H), 3.95 (t, J=6.5 Hz, 2H), 5.88 (s, 2H),6.76 (d, J=9.1 Hz, 1H), 7.08 (dd, J=9.0, 2.9 Hz, 1H), 7.55 (d, J=2.9 Hz,1H).

Compound 3 was prepared by placing compound 2 (1.1914 g or 5 mmol), ironpowder (2.7925 g, 10 eq, 50 mmol), and ammonium chloride (2.674 g, 10eq, 50 mmol) in a round bottom flask. Isopropanol (approximately 40 mL)was added to the flask until compound 2 dissolved. Then formic acid (19mL, 100 eq, 500 mmol) was added slowly. The resultant mixture was raisedto 90° C. and stirred under Ar(g) for three hours. The mixture wascooled to room temperature. Iron powder was separated by filtration andwashed with 3×15 mL of isopropanol. Combined filtrates were collectedand reduced under vacuum. The resultant residue was mixed with NaHCO₃until all of the remaining formic acid had reacted. The reaction mixturewas partitioned with dichloromethane and its non-aqueous layer wascollected. The aqueous layer was washed three times withdichloromethane. Combined non-aqueous layers were dried over MgSO₄,filtered, and reduced under vacuum. A deep-orange solid was obtained(compound 3, 69% yield).

¹H NMR (CDCl₃) δ: 1.55 (m, 4H), 1.84 (m, 2H), 1.92 (m, 2H), 3.45 (t,J=6.8 Hz, 2H), 4.01 (t, J=6.4 Hz, 2H), 6.89 (dd, J=9.1, 1.9 Hz, 1H),7.14 (d, J=1.9 Hz, 1H), 7.59 (d, J=1.9 Hz, 1H), 8.21 (s, 1H)

Compound 4 was made by placing compound 3 (0.7429 g, 2.5 mmol) in a dryround bottom flask with NaN₃ (0.1788 g, 1.1 eq, 2.75 mmol) and 25 mL ofdry dimethylsulphoxide (DMSO). This mixture was stirred at roomtemperature for 4 hours. Reaction progress was followed by this layerchromatography. When all of the starting material was consumed, asaturated solution of NaHCO₃ (50 mL) was added to the mixture. Themixture was then filtered and the filtrate was removed. The resultantsolid was washed with 3×25 mL of dichloromethane and its filtrate wascollected and reduced under vacuum. Deep-orange solid was obtained(compound 4, 67% yield). ¹H NMR (CDCl₃) δ: 1.50 (m, 4H), 1.66 (q, J=7.2Hz, 2H), 1.84 (q, J=7.1 Hz, 2H), 3.30 (t, J=6.8 Hz, 2H), 4.00 (t, J=6.4Hz, 2H), 6.95 (dd, J=8.7, 2.3 Hz, 1H), 7.11 (d, J=2.1 Hz, 1H), 7.56 (d,J=8.9 Hz, 1H), 8.02 (s, 1H)

Compound 5 was made by taking 0.388 g of 4 (1.5 mmol) and 0.4887 g ofCs₂CO₃ (1 eq, 1.5 mmol) in a dry pressure tube under Ar(g). Acetonitrile(5 mL) was added followed by 3.75 mL of isopropyl iodide (25 eq, 37.5mmol), which was added drop-wise. The tube was then sealed with aTEFLON® lid. The reaction flask's temperature was raised to andmaintained at 90° C. and the mixture was stirred overnight. The tube wasallowed to cool to room temperature, and NaBF₄ (1.647 g) was addedquickly. The tube was resealed and allowed to stir for 48 hours. Themixture was filtered and the collected solid was washed withdichloromethane. Combined filtrates were collected and their volume wasreduced under vacuum. A crude sticky solid of compound 5 was crystalizedusing a mixture of ethyl acetate and hexane. This solid was useddirectly in the next step without further purification. ¹H NMR (CDCl₃)δ: 1.55-1.68 (m, 8H), 1.89 (quart, J=3.3 Hz, 12H), 3.33 (t, J=6.6 Hz,2H), 4.10 (t, J=6.2 Hz, 2H), 5.13 (m, 2H), 7.12 (s, 1H), 7.24 (s, 1H),7.66 (d, J=9.1 Hz, 1H), 10.53 (s, 1H).

Compound 6 was prepared by taking the product 5 and adding 0.102 g ofKHCO₃ in 5 mL of dry methanol in a TEFLON® capped vial. This was allowedto stir at room temperature for 48 hours. After this the mixture wasreduced under vacuum and 5 mL of dichloromethane was added. This wasthen filtered through celite and crystalized with hexanes to give asticky residue. This was then washed with more hexanes with sonicationto give the solid 6. ¹H NMR ((CD₃)₂CO) δ: 1.50 (m, 2H), 1.57 (m, 2H),1.66 (m, 2H), 1.80 (m, 12H), 1.88 (m, 2H), 3.37 (t, J=6.4 Hz, 2H), 4.23(t, J=6.4 Hz, 2H), 5.24 (m, 2H), 7.34 (d, J=9.4 Hz, 1H), 7.68 (s, 1H),8.04 (d, J=9.4 Hz, 1H), 10.02 (s, 1H)

NHC-7 was made by taking compound 6 (1.88 mg) and dissolving it in drymethanol (4 mL). This solution was then added to a vial housing agold-on-mica chip (available from Georg Albert PVD—Beschichtungen ofHauptstr, Germany). The vial was sealed with a TEFLON® cap. The vial andits contents were left to sit overnight. The next morning, the gold chipwas washed with 150 mL of methanol and dried. XPS of the chip's surfacewas then measured. XPS ratio: N_(BZMDZ):N_(AZL):N_(AZC):C_(R):C_(Ar) is2:2:1:14:8, overall 5 nitrogen atoms per 22 carbon atoms, which is closeto stoichiometric ratio (2:2:1:12:7).

NHC-8 was made by dissolving KOtBu (0.002 g) in 2 mL of dry DMSO. Thenphenyl acetylene (0.01 mL) was added and the solution was swirled tocombine. NHC-7 was submerged in the solution and the vial was sealedwith a TEFLON® cap and the mixture was allowed to sit overnight at roomtemperature. The gold surface was then washed with 150 mL of methanoland dried.

NHC-9 was made by placing diphenyliodonium tetrafloroborate salt (0.037g) and CuSO₄ (0.8 mg, 5 mol %) in a vial and dissolving them in 2 mL ofdimethylformamide (DMF). NHC-8 was then added to the solution and thevial was sealed with a TEFLON® cap. The vial's contents' temperature wasraised to and maintained at 100° C. overnight. In the morning, the vialwas cooled to room temperature and the gold chip was washed with 150 mLof methanol and dried. XPS of this surface is in progress.

NHC-10 was prepared by placing NHC-9 in a Schlenk flask and placing itin a glove box having an Ar(g) atmosphere. Then 10 mg of [IrCp*Cl₂]₂ wasadded to the flask with a minimal amount of dry tetrahydrofuran (THF).NaHMDS (Sodium bis(trimethylsilyl)amide also known as sodiumhexamethyldisilazide ((CH₃)₃Si)₂NNa) (18 mg) was added to a separatevial. It was dissolved in THF and the vial was capped with a rubberseptum. The Schlenk flask and the vial were then removed from theglovebox. The Schlenk flask was placed under Ar(g) following standardSchlenk line techniques and was cooled to −78° C. using a dry ice bath.After 10 minutes, the NaHMDS solution in the vial, which was also underan Ar(g) atmosphere, was added to the Schlenk flask drop-wise viasyringe. The resultant solution was allowed to come slowly to roomtemperature overnight. The next morning the gold chip was removed fromsolution, washed with 150 mL THF, and dried. XPS of this surface is inprogress.

Example 11. Click Reaction of Mixed Monolayer

An experiment was performed wherein NHC-8 was present in 25% on a goldsurface and the remaining SAM consisted of a 6-carbon chain alkylderivative (collectively designated NHC-11 in Table 1). A click reactionwas performed on this surface and was deemed successful. That is, theclick reaction occurred at NHC-8 and not at the 6-carbon derivative.Thus a “diluted” catalyst can be used where only 25% of the molecules onthe surface are the active catalyst (with iridium), the other 75% beinga “filler” which is similar to the catalyst. The presence of the“filler” allows the mixture of catalyst and filler to form a SAM sinceinteractions between the catalyst and the filler are similar tointeractions between the catalyst and another catalyst. The experimentalratio shown below supports that the mixture was deposited in the sameratio that the compounds (catalyst and filler) were mixed in (25:75ratio). XPS of this monolayer of mixed carbenes had an expected ratioC:N of 21.7:2.7, and an observed ratio of 23:3.

Example 12. Water Oxidation Studies Using Cerium Ammonium Nitrate and UVAbsorbance Detection

These experiments are intended to demonstrate that NHC-terminated metalsamples are capable of oxidizing water. A sacrificial oxidant, ceriumammonium nitrate (“CAN”), was used both to complete the oxidation cycleand to track the progress of reaction by monitoring a UV-vis peak thatis characteristic of the unreduced CAN.

In a first experiment, a NHC-terminated gold on mica sample was placedin a fresh solution of 7.5 mM cerium ammonium nitrate (CAN) in 0.5 Mnitric acid (“acid” on FIG. 18A) in a quartz cuvette. The gold sampleswere coated with 100% NHC-15, 25% NHC-10 and 75% NHC-15, or 100% NHC-10.The cuvette was placed in a UV-vis spectrometer and the absorbancemeasured every 15 seconds for 6 hours at a wavelength of 420 nm. It wasobserved that the concentration of CAN decreased, and bubbles wereformed, as time progressed; these results are indicative of wateroxidation (see FIG. 18A).

In a second experiment, a 10 mL solution of 7.5 mM ceric ammoniumnitrate (CAN) in 0.5M HNO₃ was prepared fresh and 3.8 mL of the solutionwas added to a quartz cuvette. A NHC-terminated gold on silicon samplewas placed in the solution, and coated with 100% NHC-15. The solution'sabsorbance was measured every 15 seconds, for 3 hours, at a wavelengthof 420 nm. Following this, 15.6 mg of CAN was added directly to thecuvette and absorbance was again measured every 15 seconds for 3 hoursat 420 nm. This was repeated until a total of 5 runs in total weremeasured (See FIG. 18B).

Example 13. NHC Deposition on Nickel and Tungsten

Nickel (Ni) foil was cut into pieces 1 cm². Tungsten (W) wire (2 mmdiameter) was cut into 1 cm lengths. These metal samples were cleanedwith acetone and then ethanol. A solution of carbonate salt of NHC-1(1-2 mmol) was prepared in ethanol. The Ni foil and W wire samples wereeach immersed into 5 mL of the NHC-1 solution for a period of 24 hoursat 25° C. Each Ni and W sample was then removed from their respectivesolutions, rinsed with ethanol and air-dried. Resulting XPS spectraindicated that NHC-1 had deposited on the metal's surface. See FIG. 19.

Example 15. Stability of Carbene Monolayers in Decalin at 100° C. and190° C.

NHC-1 functionalized surfaces were placed in Ace Glass pressure tubes,and 2 mL of decalin was added. The tubes were purged with nitrogen gas,sealed and heated at either 100° C., or 190° C. for 24 h. After thistime, the samples were cooled to room temperature, rinsed with hexane(2×5 mL), ether (2×5 mL), and ethanol (2×5 mL), dried under a nitrogengas stream, and analysed by XPS. The samples treated at 100° C. showedno discernible change, while the samples treated at 190° C. showeddecomposition (see FIGS. 21A and 21B).

TABLE 1 Structural information for NHCs on metal. Nickname StructureName of NHC/salt Prepared from NHC-1 on gold

1,3-dihydro-1,3- bisisopropyl- benzimidazol-2- ylidene (also known as“IPrBenz”)

Monolayer prepared using hydrogen carbonate salt of NHC-1

1,3-dihydro-1,3- bisisopropyl- benzo[d]imid- azolium hydrogen carbonate

NHC-2 on gold

2,4-dihydro- 2,4,5-triphenyl- 1,2,4-triazol-3- ylidene (also known as“Enders' carbene”)

Monolayer prepared using hydrogen carbonate salt of NHC-3

1,3-dihydro-1,3- bis(2,4,6- trimethylphen- yl)imidazolium hydrogencarbonate

NHC-3 on gold

1,3-dihydro-1,3- bis(2,4,6-tri- methylphen- yl)imidazol-2- ylidene (alsoknown as “IMes”);

NHC-4

1,3-bis(2,4,6- trimethylphen- yl)imidazolin-2- ylidene (also known as“SIMes”)

NHC-5A

1,3-dihydro-1,3- bis(2,6- diisopropyl- phenyl)imidazol- 2-ylidene (alsoknown as “IPr”)

Monolayer prepared using hydrogen carbonate salt of NHC-5A

1,3-dihydro-1,3- bis(2,6- diisopropyl- phenyl)imidazol- ium hydrogencarbonate

NHC-5B on gold

1,3-bis(2,6- diisopropylphen- yl)imidazolidine- 2-

NHC-6 on gold

1,3-diisopropyl- 5-(12- (azido)dodecyl- oxy)-1H- benzo[d]imidaz-ole-2-ylidene

NHC-7

5-(6- azidohexyloxy)- 1,3-diisopropyl- 2,3-dihydro-1H- benzo[d]imidaz-ole-2-ylidene

Monolayer prep'd using hydrogen carbonate salt of NHC-7

5-((6- azidohexyl)oxy)- 1,3-diisopropyl- benzo[d]imidaz- olium hydrogencarbonate

Product of click chemistry on NHC-6, which is referred to herein asNHC-6A

NHC-8

NHC-9

NHC-10

NHC-11

Monolayer prep'd using hydrogen carbonate salt of NHC-13

1,3-diisopropyl- perimidinium hydrogen carbonate

Monolayer prep'd using hydrogen carbonate salt of NHC-14

1,3-diisopropyl- naphtho[2,3- d]imidazolium hydrogen carbonate

NHC-15

5-(hexyloxy)- 1,3-diisopropyl- 2,3-dihydro-1H- benzo[d]imidaz-ol-2-ylidene

Monolayer prep'd using hydrogen carbonate salt of NHC-15

5-(hexyloxy)- 1,3-diisopropyl- benzo[d]imidaz- olium hydrogen carbonate

NHC-16

5-(dodecyloxy)- 1,3-diisopropyl- 2,3-dihydro-1H- benzo[d]imidaz-ol-2-ylidene

Monolayer prep'd using hydrogen carbonate salt of NHC-16

5-(dodecyloxy)- 1,3-diisopropyl- benzo[d]imidaz- olium hydrogencarbonate

Monolayer prep'd using hydrogen carbonate salt of NHC-17 on gold

1,3-dimethyl- benzo[d]imidaz- olium hydrogen carbonate

Monolayer prep'd using hydrogen carbonate salt of NHC-18, on gold

1,3-diethyl- benzo[d]imidaz- olium hydrogen carbonate

NHC-18 on gold

1,3-diethyl-2,3- dihydro-1H- benzo[d]imidaz- ol-2-ylidene

TABLE 2A XPS data for products obtained by reacting NHCs withAu(111)surfaces and Au nanoparticles N:C ratio (XPS) Carbene Found NHC on GOLDExpected Au(111) Au_(NP) NHC-1 2:13 2:14 2:13 NHC-2 3:20 3:21 3:22 NHC-32:21 2:21 2:23 NHC-4 2:21 2:22 2:22 NHC-5A 2:27 2:29 2:27

TABLE 2B C and N XPS spectra for the carbonate salts of various carbenesself-assembled on Au. N:C ratio Expected Found NHC-1 2:13 2:13 NHC-32:21 2:22 NHC-5A 2:27 2:27 NHC-5B 2:27 2:26 NHC-7 5:19 5:22 NHC-13 2:172:17 NHC-14 2:17 2:17 NHC-15 2:19 2:18 NHC-16 2:25 2:26 NHC-18 2:11 2:12

TABLE 4 Characterization of NHC-1-substituted Pd nanoparticles.Stabilizing Pd Agent XPS Peak nanoparticle Nanoparticle ConcentrationPosition N:S C:N sample diameter (nm) (mM) N 1 s S 2 p ratio ratio PdNP-X-NHC 1.5-2.5 2.0 400.06 163.06 2.6:1 7.7:1 Pd NP-Y-NHC 2.5-4  0.5400.65 163.46 4.8:1 7.3:1 Pd NP-Z-NHC  4-5.5 0.12 400.21 163.09 6.7:113.5:1 

TABLE 5A Loading of HPA sensor chip and NHC-16 Carbene sensor chip withPC (phosphatidylcholine) SUV (35 nm) for 4 cycles in the listed buffer.Initial loading Loading Initial (RU) after NaOH BSA Sensor loading Afterbulk shift wash bound Buffer pH chip (RU) subtraction (RU) (RU) Citrate5.0 HPA 3924 ± 222 3789 ± 217 2598 ± 145 274 ± 85 (5.66%) (5.73%)(5.58%) (31.02%) Carbene 1893 ± 50 1523 ± 41 1449 ± 31 101 ± 9 (2.64%)(2.69%) (2.14%) (8.91%) PBS 7.4 HPA 9340 ± 391 8930 ± 386 1579 ± 25 60 ±38 (4.19%) (4.32%) (1.58%) (63.33%) Carbene 1671 ± 41 1530 ± 24 1325 ±34 54 ± 8 (2.45%) (1.57%) (2.57%) (14.81%) HEPES 8.0 HPA 2600 ± 543 2350± 539 1348 ± 24 22 ± 12 (20.88%) (22.94%) (1.78%) (54.55%) Carbene 1244± 26 991 ± 31 909 ± 32 79 ± 4 (2.10%) (3.13%) (3.52%) (5.06%) TE 8.0 HPA804 ± 33 563 ± 40 516 ± 40 212 ± 13 (4.10%) (7.10%) (7.75%) (6.13%)Carbene 937 ± 30 662 ± 36 592 ± 27 96 ± 4 (3.20%) (5.44%) (4.56%)(4.17%) CAPS 10.0 HPA 846 ± 32 571 ± 18 451 ± 14 309 ± 9 (3.78%) (3.15%)(3.10%) (2.91%) Carbene 1366 ± 18 1063 ± 20 939 ± 33 42 ± 5 (1.31%)(1.88%) (3.51%) (11.90%)

TABLE 5B Chip Stability Test: Loading of HPA sensor chip and Carbenesensor chip with PC SUV (35 nm) for 4 cycles after 24 h 65° C. in ovenin PBS buffer (pH 7.4). Initial loading Loading Initial (RU) after NaOHBSA Sensor loading After bulk shift wash bound Buffer pH chip (RU)subtraction (RU) (RU) PBS 7.4 Carbene 1880 ± 22 1502 ± 19 1364 ± 54 61 ±9 24 h 65° C. (1.17%) (1.26%) (3.96%) (14.75%)Notes on Tables 5A and 5B:Values given as response units with standard deviations (SD) andrelative standard deviations (RSD) for n=4.Lower percentage indicates a lower variability in the data set. Equally,higher percentage indicates the data set is more varied.PBS: 100 mM Na₂HPO₄/NaH₂PO₄, 150 mM NaCl.Citrate: 100 mM Citric acid/Na₂HPO₄.HEPES: 10 mM N-(2-hydroxyethyl) 1-piperazine-N′-(2-ethanesulphonicacid), 100 mM NaCl.TE: 10 mM Tris-HCl, 1 mM EDTA.CAPS: 10 mM 3-(Cyclohexylamino)-1-propanesulfonic acid, 150 mM NaCl.

All publications, patents and patent applications mentioned herein areindicative of the level of skill of those skilled in the art to whichthis invention pertains and are herein incorporated by reference to thesame extent as if each individual publication, patent, or patentapplications was specifically and individually indicated to beincorporated by reference.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

We claim:
 1. A carbene-functionalized composite, comprising:1,3-dihydro-1,3-bisisopropyl-2H-benzimidazol-2-ylidene carbene coatingon a flat metal surface on a support; wherein the metal is selected fromthe group consisting of gold, palladium, platinum, and ruthenium, andwherein the 1,3-dihydro-1,3-bisisopropyl-2H-benzimidazol-2-ylidenecarbene interacts with the metal surface to form a densely packedcarbene monolayer coating that exhibits long-range ordering and isthermally stable at 100° C. for 24 hours, and wherein the metal surfaceis selected from the group consisting of bulk metal, solid metal,atomically ordered metal surface, metal film, metal sheet, and metallayer, and is not a nanoparticle.
 2. The composite of claim 1, whereinthe carbene monolayer coating comprises ≤5% contamination.
 3. Thecomposite of claim 2, wherein the carbene monolayer coating comprises≤2% contamination.
 4. The composite of claim 1, wherein the support ismica, alumina, silica, titania, silicon, glass, indium tin oxide, or anycombination thereof.
 5. The composite of claim 1, wherein the compositeis a surface plasmon resonance (SPR) detector chip.
 6. The composite ofclaim 1, further comprising a non-metal surface.